Jeff Nelson, vegsource.com | 08/19/12
Newsletter subscribers recently wrote to me citing two scientific reviews on nuts and weight. An expert had told them these reviews showed that “90% of published studies suggest that nut consumption does NOT lead to weight gain.”
They wanted to know what I thought, since I recently wrote about nuts and weight loss.
The answer is that the two scientific reviews didn’t show that nut consumption doesn’t lead to weight gain. In fact, they show just the opposite, that nuts cause weight gain.
The reviews also expose the worst side of the nut industry – their pathetic attempts to “buy” bogus science in order to sell nuts.
What did they do? They took a whole lot of cholesterol/nut studies to try to show nuts don’t cause weight gain. In these cholesterol/nut studies, whenever nut-eating subject’s weight went up on any given day, the researchers immediately cut their calories, in order to make their weight go right back down. These studies where weight was controlled and manipulated as part of the study have been presented by the nut biz as “proof” nuts don’t cause weight loss. You may be surprised which doctors and dietitians fell for this scam. Read on to see how the nut biz almost got away with it.
The first review sent to me is actually one I’ve previously debunked. It’s a review of other studies called:
A review of the evidence: nuts and body weight. Natoli S, McCoy P. Asia Pac J Clin Nutr. 2007;16(4):588-97. Food and Nutrition Australia, NSW, Australia.
Here is a link to the full study: http://www.findthatpdf.com/download.php?i=9208316&t=hPDF
Okay, here’s the bottom line: this is a review of 22 studies on nuts. It’s funded by the nut industry, and contrary to how it’s been hyped – as the “gold standard” showing nuts do not cause weight gain – the study actually very clearly shows that nut consumption does cause weight gain.
The Review authors also use a very sneaky trick to try to imply the opposite, which I’m going to expose in a moment. And if a doctor or dietitian doesn’t carefully read this, they could be duped by these kinds of reviews, as several have been – even some in the veg world.
Who paid for it?
So first, let’s look at the “Acknowledgements” section of this Review, on page 393, and we can see who paid for it:
As you can see, funding for the Review came from the Australian Tree Nut Industry, and the Horticulture Australia Limited organization (HAL). HAL describes itself as an industry-owned nonprofit organization that invests in research and marketing, see: http://www.horticulture.com.au/about_hal/default.asp The rest came from matching funds by the Australian government.
Next, before getting into the Review details, let’s look at the Abstract for the authors’ major findings. Click to enlarge:
The findings show that the role of nut consumption in body weight management is varied. Nuts, when included as part of an energy-controlled diet, were found in some instances to assist with weight loss. However, when nuts were added to an existing diet without controlling for energy intake, body weight increased, although to a lesser extent than theoretically predicted.
So what is the story when it comes to nuts and weight, according to this important “gold standard” Review?
It is simply that if you add nuts to your diet, you are going to gain weight. Period end of subject.
Given that this is what the authors state up front, how could people believe thisReview actually proves the opposite?
How the nut industry dupes some doctors and dietitians
The Review first lists 4 studies on nuts and weight, as I’m about to show you. And those studies show that nuts cause weight gain.
Then the Review lists 18 more studies, but they aren’t 18 studies on nuts and weight. They are 18 studies on nuts and cholesterol. As part of these cholesterol/nut studies, study subjects’ weight was recorded before and at the end of the studies.
What may be surprising, since it’s well established that nuts cause weight gain, is that looking at the data from theses nut/cholesterol studies, many of the subjects who started eating nuts – have the same weight at the end of the studies as they did at the start. They ate nuts for 2, 4 or 8 weeks of the cholesterol/nut study, and didn’t gain any weight!
You would think, if nuts cause weight gain as is well known, that the cholesterol study subjects who added nuts to their diets would have gained, right? But since most of them did not, but were the same weight at the start and finish of the study, maybe nuts do not cause weight gain, right?
And when you look at the fact that only 4 nut/weight studies in the Reviewshowed weight gain, while 18 nut/cholesterol studies show NO weight gain, it starts to look like the nut-lovers finally have a study to back them up.
And that is probably as far as the nut-advocate doctors read in this Review before they started screaming the “results” from their rooftop.
But here’s the problem.
Cholesterol researchers cannot permit their nut-eating study subjects to gain weight. Ever.
Gaining weight can influence cholesterol levels. If you’re trying to test whether nut consumption influences cholesterol levels, you had better make absolutely certain people in your studies do not gain any weight, lest your cholesterol results be influenced and your study rendered worthless by that weight gain.
So what do cholesterol researchers do?
Simple: they use a scale with their nut-eating study subjects. And they don’t allow them to gain any weight at all.
You see, cholesterol researchers design their studies so that the nut-eating subjects are being weighed, usually every day. And usually right before dinner. And when the nut-eaters gain some weight, as of course they do – they’re adding nuts to their diets after all – then the dietitian controlling the study subjects’ food will feed that nut-eater less food that night. And those nut-eaters will continue to receive less food until their weight goes back down to normal.
This isn’t a secret. It’s described in just about every cholesterol study in this Review of the evidence: nuts and body weight, as you are about to see.
So the truth is, in a cholesterol study where subjects are fed nuts, the subjects’ before/after weight doesn’t tell you a thing about whether nuts cause weight gain. It’s all up to researchers to decide whether subjects gain weight, and as you’re going to see in all these cholesterol/nut studies, they always forbid and prevent weight gain.
So why would the nut-industry-paid reviewers include 18 studies in a review about nuts and weight, when they know that the nut-eaters weight in those cholesterol studies was meaningless? That’s a very good question, and the answer is probably that unfortunately, many doctors and dietitians don’t actually read the studies they promote, and the nut industry relies on that.
The Review Layout
As you can see from the link to the study above, the layout of the data in this Review of the Evidence: Nuts and Weight is split into two sections, two Tables.
Table 1 examines 4 studies that actually were set up to test whether nuts add weight. These were correctly set up weight studies where researchers didn’t manipulate the subjects’ diet, but merely let subjects eat nuts like you or I would in real life. As you will see, those weight/nut studies show an undisputed fact: adding nuts to your diet causes weight gain.
Then authors of this nut industry-funded Review of the Evidence: Nuts and Weight do this very strange thing. They don’t list any more weight/nuts studies, but instead list the 18 cholesterol/nuts studies, and the fun gets going.
I just have to say, to title an article Review of the Evidence: Nuts and Weight, and then to focus the Review almost entirely on studies whose design was to prevent nut-eaters from gaining weight… Does this sound like scientific fraud to anyone else?
It’s worth mentioning, too, that not only was this Review of the Evidence funded by the nut industry, but most of the studies looked at in the Review were as well.
So now let’s look at the 22 studies that this Review examined and see how they did it.
Table One – Do Nuts Cause Weight Gain? Yes!
Here is Table 1 from the Review, you can click on the image to see a larger version. As noted, the studies in Table 1 are the only part of the Review that looked at studies actually devised to examine the question of whether nut consumption causes weight gain:
Table 1 shows 4 different studies on nuts and weight. In studies A, B and D, you can see under the “Conclusion” column at right that subjects eating nuts all gained weight when they simply added nuts to their diets, just as the authors said would happen.
Subjects seemed to gain an average of about one pound in 6 months, which is consistent with other studies looking at nut consumption – you gain about 2 pounds a year if you simply add nuts to your diet without doing anything else to your diet, such as restricting calories. (Since this 2 pounds a year weight gain is an average, this means if one person doesn’t gain 2 pounds in a year eating nuts, someone else gains 4 pounds.)
The third study above, Study D, was a study where obese and ill patients of the 24-week Diabetes and Cardiovascular Risk Reduction Programwere put on low calorie liquid diet formulas. Half the group was put on a low calorie liquid diet which contained almonds; the other half was put on a low calorie liquid diet which didn’t contain almonds but instead had a higher amount of complex carbohydrates.
That full Study D is available here:
Both liquid diet groups lost substantial weight, but the group drinking the formula with the almonds lost slightly more weight in 6 months than the higher complex carb formula drinkers.
Importantly, the group consuming the liquid diet with almonds had their blood keytone levels go through the roof, as the study shows. In the absence of sufficient calories or sufficient carbohydrates, which is the body’s preferred fuel, the body burns fat, releasing ketones. (This is how low-carb, high-protein diets work, as well.) This explains the slightly improved weight loss numbers of the high-fat almond group as it shows they were experiencing a larger calorie deficit, and were in ketosis.
But all of that aside – what relevance does a study of sick obese people drinking low calorie liquid diets for six months have on anyone in the general public wondering about nuts and weight loss? The answer is: precious little. It’s known that not all calories estimated to be in nuts are absorbed by the body, but when people add nuts to their diet, they still gain weight. A study where all subjects are being underfed a liquid medical diet is rather meaningless to the question of nuts and weight for the average healthy person.
So to review, Table 1 lists the only studies in this Review which had been designed and controlled to look at weight gain and nuts, and they overwhelmingly show that adding nuts to one’s diet will cause weight gain.
Table 2 — Let the product propaganda begin
Here are the first 13 of those 18 studies, from Table 2. Again, click to see a larger version:
Now the far right column on this Table is once again “Conclusion.” And if you scan through the conclusions of each of these cholesterol studies, you might be taken by the fact that in many of these nut/cholesterol studies, the nut-eating subjects did not gain weight!
This is where some doctors and dietitians stopped reading and started promoting nuts as not causing weight gain.
By now you know they were wrong.
Of these 13 studies in Table 2, note the column labeled “Diet Energy Controlled.” Note that all but 2 of the studies are labeled “Yes – isogenic.” I have circled the words “yes – isoenergetic” in blue above.
So these are diets where the food subjects ate was controlled and manipulated by the researchers, so that people would not gain weight when they added nuts to their diet.
Let’s take a look at each of these studies now to see how the nut-eaters weight gain was reversed and their ending weights brought back to “normal” by the researchers.
From Table 2 in the Review above, let’s look at Study #1. Here is a copy of that full study:
In this study, subjects were fed a reference diet, or a reference diet where walnuts were added – and other foods from the reference diet were removed to compensate. The authors state:
“Body weight as measured without shoes or heavy clothing was recorded every day during the run-in period and twice a week thereafter; energy intake was adjusted when necessary to maintain weight. Average body weight decreased by 1.4kg over the 61 days of the study, but this decrease was not related to a specific diet.”
So researchers weighed the subjects daily and “adjusted” how much food they were eating if they started to gain or lose weight.
In Study #2, a total of 16 subjects were put on three different diets, a nut-free reference diet, a diet which included walnuts, and a diet which included almonds. You can see this full study here:
Researchers designed the diets so that the calorie intake for each of the three would be equal, so that no one would gain weight. Here is a line from the study’s Discussion:
“The three diet periods were well matched for total energy intake and major dietary components, as reflected in the stable body weight throughout the study.”
So researchers controlled the outcome of subjects’ weight by matching the calories to make sure subjects’ weight didn’t change during the study.
Let’s look at Study #3 above. I have uploaded a copy of the study here:
Subjects were either put on a control diet, or a diet high in fruits, vegetables and nuts. Under “Subjects and Methods,” the authors report:
“Body weight was measured by the investigators, and fasting blood samples and 24-hour urine output were collected before the start and at the end of week 2 of each dietary phase. In addition, subjects were also asked to weigh themselves on a daily basis during the study periods and to report any consistent trend in weight change so that diets and caloric intakes could be modified at the end of the first week to maintain weight.”
So the study subjects were told to weigh themselves every day, and if they started to gain weight, the researchers then modified their caloric intake during the study so that they would keep their weight the same as when they started the nut diet.
Let’s look at Study #4. In this study, 48 individuals were placed on 1 of 3 diets designed by the researchers, one almond-based, one olive oil-based, one dairy-based for 4 weeks. The study is available here:
From the study:
“Total fat in each diet was matched, and the study-provided sources of fat comprised the major portion of fat intake… Weight did not change.”
Although this was another calorie-controlled study where researchers kept the diets equal in calories, if you look at Table 3 of this study, you will note that those on the Almond-based diet had their weight stay the same at the end of the 4 week study period, whereas those on the olive oil-based and control diets each LOST a small amount of weight compared to the nut-eaters. So although the fat in each diet was kept the same, those eating nuts were the only group that didn’t lose weight. It was a small effect, but it happened – nut-eaters lost less weight than those not eating nuts.
So this is another study designed to rig the diets so the nut-eaters didn’t gain weight.
Let’s look at Study #5 above. You can download this full study here:
This study looked at people on a pistachio diet versus people who did not consume nuts during the three week study period. Researchers state in the “Dietary Intervention” section:
“Half of these patients were placed on a pistachio diet. This involved substituting roasted, unsalted pistachio nuts for 20% of their daily caloric intake. The subjects otherwise consumed the components of their regular diets. Subjects who normally consumed high fat snacks were instructed to substitute the pistachios nuts. If a subject did not normally consume high fat snacks, pistachio nuts were substituted as fat calories.”
So to test the pistachio diet, subjects had to give up a regular high fat snack in place of the nuts, or else give up other fat calories in their diets in order to compensate for the extra nut calories, according to the study protocol.
Do you see what’s going on here? When doing a Review of the Evidence: Nuts and Weight, just be sure to pick a bunch of nut studies where nut-eaters were physically prevented from gaining weight, if your object is to try to confuse people into thinking nuts don’t cause weight gain.
So on to study #6 above. Researchers report under “Conclusion” that the participants’ weight was maintained within 1kg (or 2.2 pounds) during the study period. You can download the full text of this study in PDF here:
Here is the interesting part about study #6:
Subjects were randomly assigned to receive one of five experimental diets. Over the course of the study, each subject consumed each diet. Subjects ate breakfast and dinner at the Metabolic Diet Study Center Monday through Friday, and lunches and weekend meals were packed. Subjects consumed an amount of food consistent with their energy needs and they were weighed every day during the week before dinner to ensure that weight was maintained.
Subjects who were eating nuts were weighed before each meal, and then given an amount of food “consistent with their energy needs.” That means if a participant started to gain weight because of the added nuts or nut oil they were fed, they were given less food by the researchers feeding them, until their weight came back down to where it had started. Just like the rest of the cholesterol studies in this “weight” review.
Continuing, here is study #7, you can read it online here:
Study subjects ate either a standard diet or a macadamia-enriched diet. Under “Study & Methods,” the authors write:
Every day, the subjects ate breakfast and dinner at the study site and were given a bag lunch prepared by study personnel. The one exception was Saturday night, when participants were allowed a “free” meal with specific guidelines on the amount of fat consumed. Additional energy was made available in the form of “unit” foods consumed ad libitum in addition to the subjects’ diet regimen, as long as they maintained their weight. These were in the form of 420-kJ (100-kcal) muffins or 420- and 840-kJ (100- and 200-kcal) packages of chili, developed to match the nutrient profile for each diet. Body weight was measured 2 times per week, and energy intake levels were altered when necessary to maintain each subject’s weight.
So once again, in order to suggest that nut consumption doesn’t promote weight gain, the author of this highly touted Review has selected a study where nut-eaters were weighed twice a week, and when they had gained weight, their food was adjusted down until their weight went back down, so that by the end of the study there was no weight gain recorded.
Study #8 I have put online here:
This is the first study in Table 2 which is not an isogenic diet. Two groups were free to eat what they wanted for 8 weeks, with the pecan treatment group consuming up to 68g of pecans per day.
This is the first and only study so far, that showed no weight gain when the nut group was tested against the non-nut control group. But note what the authors said under “Discussion”:
“Body weights as measured by BMI remained unchanged in spite of increases in energy intakes in the pecan treatment group. This is surprising and would not be expected to continue if the higher energy intakes were sustained by pecan consumption over an extended period of time. Had the study continued for a longer time, weight gain could have emerged as a result of the higher energy intakes associated with pecan supplementation. Exercise was not measured for duration and intensity. Differences in energy expenditure may have been a contributing factor to the stable BMI observed in the pecan treatment group during the course of the study.”
Unfortunately, this was designed to be a study investigating nuts consumption and cholesterol. Had it been a study to examine nuts and weight, it would have been designed differently, to take into account things like the age and physical condition of people in both groups, exercise levels of both groups, and what the actual diets of both groups were comprised of, and several other factors present in good weight studies.
Also, this was very small study, with only 13 subjects adding pecans to their diets for 8 weeks. Of those 13 pecan-eating subjects, 3 were removed from the study at the conclusion after looking at their results because, researchers say, “they were not able to conform to the study protocols; their data were not included in the statistical analyses.”
Now this is rather curious. Almost a fourth of study participants who added pecans to their diets – were eliminated at the end of the study and their data not included because they didn’t “conform.” “Conforming” meant simply eating whatever they wanted, and adding pecans to their diets. How didn’t these pecan-eaters conform? Did they fail to eat all the nuts? Did they gain weight which the researcher felt indicated they hadn’t “conformed?” Did their cholesterols go up rather than down slightly?
The study authors do not share this information, but it undercuts the study when nearly 25% of this tiny group of pecan-eaters who finished the study, were subsequently eliminated from the study and their data tossed out.
All in all, this 9-person study provides no useful information about weight and nuts. To the authors’ credit, she notes that a longer study, or a study which took into account activity levels and exercise, would likely give a different result.
This small study is the kind that is suggestive of further research, to see if someone could duplicate any of these results. Certainly the very wealthy nut industry, which has funded scores if not hundreds of expensive studies, has plenty of money to repeat a study like this. And yet, they have not. Or if they did, they probably got a different result, as the author here suggested, and chose not to publish the results.
Study #9 is available to read online here:
This was a six-week cholesterol study of the Mediterranean Diet versus a diet of the same calories and fat containing almonds. As usual, the authors set out to prevent weight gain in designing the diets. From the “Discussion”:
“Because body weight was not modified, our findings [on cholesterol lowering] cannot readily be attributed to changes in body weight or caloric intake.”
So study designers here once again deliberately worked to prevent weight variances. And again, do you see how sleazy it was for the author of this Review of the Evidence: Nuts and Weight to select all these studies that were intentionally set up to manipulate the subjects’ diet and prevent weight gain in nut-eaters from occurring.
I discuss study #10 below in a moment.
Looking at study #11 above, the full study is here:
From the study, here is how the researchers made sure the nut-eaters didn’t gain weight:
For subjects to maintain constant body weight during the study, energy intake had to be adjusted periodically. Frequent monitoring of body weight throughout the study and subjective feelings of hunger expressed by participants were used in making the necessary adjustments in energy intake.
So again, researchers gave nut-eating subjects less energy (food) when they started gaining weight.
On to Study #12. You can download the full study #13 here:
This is a study comparing the cholesterol impact of an almond-enhanced diet versus a regular diet. Under “Subjects and Methods,” they authors write:
“A registered dietitian met with each subject to provide individualized strategies for substituting their customary dietary fat sources with almond products to maintain a total fat, energy and macronutrient composition similar to baseline levels. In addition, subjects were asked to eliminate almonds and other tree nuts from their diet other than those provided by the study for the entire 12-wk experimental period. They were further required to maintain their baseline activity patterns as well as body weight.”
So this wasn’t a study to see if you gained weight eating almonds. People in the study were REQUIRED to maintain their baseline body weight. Just as in all these other studies, if they gained weight, they were required to lose the weight during the study, so that by the end of the study, there would be no weight difference between the almond and non-almond groups.
In study #13, authors note that “Body weight reduced over study period, but not specific to diet treatments.” So let’s look at this study to see what they mean. You can download the full study here:
From the Study Design section:
Ten women and 10 men consumed the walnut diet first, and the other 20 subjects consumed the reference diet. The subjects received all their meals at the nutrition research kitchen of the university during the 61 days of the study. Breakfast and dinner had to be eaten on site in a supervised sitting. Packed lunches were provided from 11:00 to 15:00.A registered dietitian weighed and apportioned all foods for each subject.
So once again, food intake was tightly controlled with a dietitian giving each subject a specific amount of food to control whether they gain weight. The authors go on:
The two experimental diets were identical except that the walnut diet substituted two servings of walnuts per day (25 or 27 g per serving, or 52 g of walnuts per 10.0 MJ) for portions of some foods in the reference diet. The portion sizes of fatty foods, such as meat, were reduced, and the amounts of visible fat (oils, margarine and butter) were decreased, to accommodate the percentage of energy derived from the walnuts (12.5%). The California Walnut Commission (Sacramento, CA, USA) donated the walnuts.
To prevent weight gain from the nuts, they were substituted for equal amounts of other foods such as meat, oils, margarine and butter.
The dietitian responsible for limiting subjects’ food must have been a little too aggressive in his or her apportioning food based on weight, and as a result everyone in the study on average lost some weight.
Coming back to Study #10, it had this interesting conclusion:
“The low fat diet, with or without nuts, resulted in significant reduction in body weight compared to the HD [habitual diet].”
That study is available here:
As you can see under “Design,” this is a study where four diets were tested on 18 Japanese people: 1) a “habitual diet” 2) “habitual diet with walnuts” 3) a “low fat diet” and 4) a “low fat diet with walnuts.”
The people eating the habitual diet with nuts for two weeks, did not gain weight. So this is the second study suggesting that on an extremely short-term period with a small number of study participants, it’s possible someone won’t gain weight right away when adding walnuts.
But what is interesting here from the study is the quote above. When the 18 people ate a low fat diet – whether with or without walnuts – they all quickly lost a significant amount of weight.
Okay, this was a very small study and not a weight study, and it was not properly set up to control for exercise and the variables controlled in weight studies, so it can’t really be taken as a study that tells anything too important about weight.
But yet it shows clearly what healthy eaters already know – if you want to lose weight, don’t play around with nuts and nonsense – just significantly reduce the fat in your diet, and you can significantly lose weight. Just ask these 18 Japanese study subjects, or ask Chef AJ, or ask any of the many, many people who have experienced this.
Table 2 – More Manipulation
Here are the rest of the studies from Table 2 of the Review – again, these are not weight studies but more studies of cholesterol and nuts. Click to enlarge:
Of the remaining 5 studies looked at, 3 were calorie-controlled studies (circled in blue), so we can ignore them – researchers manipulated food intake to control weight, as we know. So they are meaningless to the question of whether nut consumption increases weight. Thus we can ignore studies #14, 17 and 18 on that basis.
Looking at Study #15, which is not listed as an energy contolled trial, the full text is here:
This is actually two 4-weeks studies. In the first study, participants were given almonds to add to their diets, and advised to cut down on other foods so that they didn’t gain weight:
“During the supplementation period, the subjects were encouraged to maintain their habitual diets; however, they were told how much energy (calories) was provided by 100 g almonds and were advised to reduce their energy intakes by an equivalent amount in an attempt to keep energy intake constant.”
So while the researchers did not control the diets of the nut-eaters in this study as happened in most others, the researchers advised the nut-eaters that they could easily gain weight during the study, and that the nut-eaters should keep track of their own weight and adjust their diets themselves to make sure they didn’t gain weight. Despite this, the nut-eaters gained around 2 pounds in 4 weeks.
In the second study, subjects were given a specific diet to follow which contained almonds, and were weighed periodically. When they gained more than 2kg (or 2.2 pounds) before the 4 weeks were over, they had their calories reduced so that they did not gain more than the 2.2 pounds. So this study was an isogenic (calorie-controlled) study:
“The subjects were initially assigned a total energy intake to maintain body weight, and energy adjustments were made as needed to attempt to maintain weight within 2 kg of each person’s initial value.”
In spite of the precautions of telling subjects to watch their weight and the controls of the second study, the almond eaters’ weight in both studies increased “significantly,” according to study authors.
The last study is #16, and can be downloaded here:
This was not a calorie-controlled study. It was a study to determine what impact macadamia nuts might have on lowering cholesterol in people with very high cholesterol.
17 participants replaced about 15% of their calories with macadamia nuts. Subjects were encouraged to maintain their “regular lifestyles, especially their physical activity.” At the end of 4 weeks, subjects had lost about a half of a pound. The authors of Study #16 called the ½ pound weight loss a “significant reduction.”
Unfortunately, since this wasn’t a study to examine weight control, there was no control group and no investigation into what exercise regime, what specific diet or other habits and activity these 17 men might have been doing that could impact weight. And since a particular emphasis had been made to subjects about the importance of exercising during the study, this alone could have accounted for the very small weight variance.
In any event, you would have to be pretty desperate to claim a cholesterol study like this where 17 men experienced an average of a half pound weight loss in 4 weeks – was somehow good evidence that nuts promote weight loss.
If this Study #16 were in fact promising that macadamias don’t cause weight gain, or caused weight loss, why wouldn’t the nut industry attempt to repeat this as a properly designed weight loss study during the past 9 years since this study was published? That would be very big news and would be the first such study to contradict the studies that all show nuts always cause weight gain.
As I noted in my previous article about nuts [link], it’s been established that not all calories in nuts are absorbed by the body, and that people gain less weight eating nuts than would be expected given the estimated calorie content of nuts. However, properly controlled weight studies all show that while not as muchweight is gained as expected when nuts are added to the diet, weight increases with nut consumption. The authors of this Review state the same thing in their conclusion.
The Score Card – Reviewing the Review
So let’s look at the “weight of the evidence” of this Review of the Evidence: Nuts and Weight.
Of the 4 studies in Table 1, which are about nuts and weight, 3 studies show adding nuts caused weight gain. The 4th was a study looking at very low calorie liquid diets, which in no way relates to real life.
And then there are 18 cholesterol studies in Table 2.
I am dividing all the studies in the Review between the following 6 categories:
- Weight studies showing nuts cause weight gain
- Weight studies showing nuts do not cause weight gain
- Calorie-controlled liquid diet formula studies
- Calorie-controlled cholesterol studies that show nothing about nuts and weight
- Non-calorie-controlled cholesterol studies where nuts appeared not to promote weight gain
- Non-calorie-controlled cholesterol studies where nuts appear to promote weight gain
Weight studies showing nuts cause weight gain
Weight studies showing nuts do not cause weight gain
Calorie-controlled liquid diet formula studies
Calorie-controlled cholesterol studies that show nothing about nuts and weight
Non-calorie-controlled cholesterol studies where nuts appeared not to promote weight gain
Non-calorie-controlled cholesterol studies where nuts appear to promote weight gain
So looking at the totals, out of these 22 studies, only 4 of the studies were about nuts and weight.
Of those 4 studies, 3 showed strongly that nuts increase weight gain, and the other (study D) was a low calorie liquid diet study that tolds nothing about people eating nuts in a real-world situation.
There were 16 calorie-controlled studies of nuts and cholesterol, which only showed researchers could manipulate food fed to nut-eating subjects in order to offset expected weight gain.
There was 1 non-calorie controlled cholesterol study that suggested nut consumption promotes weight gain. And there were 2 non-calorie controlled cholesterol studies that suggested nut consumption doesn’t promote weight gain. But none of these 3 were weight studies and none properly controlled for variables, and thus none can really tell anything signficant or reliable about nuts and weight, other than suggesting other possible research.
So basically, out of these 22 studies on nuts, NONE of them in any way prove that nut consumption does not promote weight gain.
Do you get that?
Experts – including doctors and dietitians – have been using this Review to say that 90% of published studies show nut consumption does not promote weight gain. In fact, zero percent of these studies show nut consumption does not promote weight gain.
100% of studies in this Review which looked at whether nut consumption cause weight gain – found that they do.
And that’s why the Review authors here were forced to state as the finding of theReview that, “when nuts were added to an existing diet without controlling for energy intake, body weight increased…”
The other study “proving” nuts don’t cause weight gain?
The other study sent to me recently which was supposed to be “proof” that nuts don’t contribute to weight gain is:
Nut consumption, weight gain and obesity: Epidemiological evidence
M.A. Martınez-Gonzalez *, M. Bes-Rastrollo Nutrition, Metabolism & Cardiovascular Diseases (2010) xx, 1e6
The study can be found online at:
This is another Review which looked at a few different epidemiological studies and tried to draw conclusions about nuts. This is not a review of studies about nuts in any way.
Researchers here looked at The Nurses Health Study, the SUN study in Spain, and the PREDIMED study on the Mediterranean diet.
These are all questionnaire-based studies. For example in the SUN study, starting in 1999 people who graduated from the University of Navarra and certain other universities in Spain, were invited to take a questionnaire about their diet, lifestyle, health, and socieodemographic variables. In October of 2006 participants filled out another questionnaire. Comparing the data from 1999 and 2006, researchers look for trends.
Since many people don’t accurately recall or report their diets, researchers had to reject several thousand participants who, for example, researchers knew couldn’t possibly be reporting their diet accurately. Many people reported calorie intakes that, if true, would have caused them to lose a whole lot of weight in 7 years; instead they had gained a lot of weight, so researchers tossed them out of the study. You can see there is always a very big “quality” and “accuracy” question with this kind of research where people try to recall what they eat and how much.
The researchers in this Review looked at the data on diet and nut consumption, and then looked at the weight increases of participants after 7 years. All participants had gained some weight in the 7 years since they first filled out their questionnaires. Researchers wanted to see whether those who reported eating nuts more frequently didn’t gain as much weight as those who reported eating nuts less often. And researchers did find that generally people who had reported eating nuts 2 or more times a week, that they had gained less weight in 7 years than those who ate nuts less frequently. So all the nut-eaters did gain weight, just a little less weight.
Now the interesting thing with these epidemiological studies is that – as we all know – correlation doesn’t equal causation. Because people who reported eating more nuts didn’t gain as much weight in 7 years as people who said they didn’t eat as many nuts, we can’t simply conclude gaining less weight was because of nut consumption.
It is well known from short term nut studies (like the Review of 22 studies dissected above) that nuts always cause weight gain, unless people are on a calorie-controlled diet. It is unlikely that the people in these large epidemiological studies were being weighed each day and having their food controlled to prevent weight gain, like nearly nearly all of the nut-eating subjects in the Review above who didn’t gain weight.
So what could be at work here? Do people gain weight eating more nuts for the first six months, but then after a certain number of years start losing weight somehow while still eating lots of nuts?
Obviously not. What is evident about the people who reported eating more nuts and not gaining as much weight – is that they were the same people who also exercised more often, didn’t smoke, and ate more fruits and vegetables and a healthier diet generally than those who gained more weight. Was it the nuts? Was it the additional exercise? Was it the increased fruits and veggies? To the nut industry, clearly it was the nuts! But understand that this Review is pure conjecture. There’s no direct evidence to support any conclusion.
This is why trying to draw conclusions about one food from epidemiological studies is so weak.
If the broccoli industry wanted to show its food to be magical as the nut industry tries, they could have researchers look at the same data from Nurses Health or SUN studies, and I expect they would find the same conclusion: people eating more broccoli gained less weight.
The banana industry could also fund such a study to try to show that bananas were magical food. We know that the olive oil industry has funded a bunch of these studies, and despite research showing that olive oil injures the endothelial layer and slows down blood flow, the olive oil industry has used these same epidemiological studies to “prove” that olive oil is a magical food to stop heart disease. (It doesn’t of course; it’s been shown the Mediterranean diet helps prevent heart disease in spite of olive oil, not because of it.)
It’s like the studies the nut industry funds to try to show that nuts can lower cholesterol. Nuts can indeed lower cholesterol – but only by a small amount, and only if you have terrible cholesterol to start with, and only if you agree to give up cheeseburgers and eat nuts instead… The potato industry could show the exact same thing with the same studies, if they wanted, that potatoes lower cholesterol when you eat them instead of cheeseburgers. And the potato industry could actually show weight LOSS with their product while lowering cholesterol, rather than the weight gain that studies show accompanies nut consumption.
If you want to lower your weight fast, get on a healthy plant-based diet and lose the high fat and calorie dense foods.
If you want to lower your cholesterol, don’t fool around with nuts or any “super foods” – that’s super nonsense. Eat a lower fat, whole food plant based diet.
And get your blood panel done, know your numbers and what they mean, and if you’re not where you need to be, consider adopting a program like Dr. McDougall’s, Dr. Fuhrman’s, Dr. Esselstyn’s, Rip Esselstyn’s or one of the healthy plant-based diets out there, and then check your results again in a month to see them fall dramatically. Know your numbers, monitor them, adopt a diet proven to bring them way down. That’s how to prevent heart disease. It has nothing to do with nuts.
Nut researchers for sale
In case you wonder who the researchers are that do studies on nuts, and how the nut industry buys research, check out this website of a professional nut researcher:
If you scroll down the front page to the About the Company section, you will see this profile, which I am copying here:
Nutrition Science Solutions provides world class service at a reasonable cost.
Dr. Mark Dreher is Chief Scientific Officer (CSO)/President of Nutrition Science Solutions, LLC in Texas. He specializes in clinical study design, scientific due diligence, technical assessments, and strategic planning with extensive experience.
Mark has worked with companies such as Mead Johnson Nutritionals, Nabisco, Inc., M&M/Mars and Frito-Lay on developing strategic research plans, coordinating advisory councils, nutrition research, and setting product nutritional profiles.
Prior to consulting, Mark was the vice president of scientific and regulatory affairs for POM Wonderful, LLC and Roll International. Mark also spent years heading up R&D for McNeil Nutritionals, LLC as a member of management/operating boards on products such as Splenda, LactAid, Viactiv and Benecol.
Mark is a member of several committees and expert panels such as Almond Board of California, Institute of Food Technologists, American Society of Nutrition, International Life Sciences Institute, and American Dietetic Association.
Mark has BS in Biochemistry from the University of California at Los Angeles and a PhD in agricultural biochemistry and nutrition from The University of Arizona.
If you google “Dreher” and “nuts,” several articles and studies he authored – touting the wonderful benefits of nuts – will come up, including studies trying to sell the industry-pushed meme that nuts don’t cause weight gain. He is apparently a reliable hand for companies looking to develop research to assist in product marketing. Just as there are advertising companies ready to help companies sell product, there are scientists for hire, too.
We all have to make a living. 🙂