We recently ran an article by Chef AJ talking about how she dropped the extra weight she had been trying to lose for years. AJ had been eating a healthy plant-based diet – that included regular rich desserts and chocolate. She says she was also eating 1.5 ounces of nuts a day. AJ said she gave up all desserts and chocolate for one year, but lost no weight. Then she gave up the nuts, and her excess weight rather effortlessly disappeared in a matter of months.
Some were surprised by AJ's success because there are studies suggesting moderate nut intake doesn't promote weight gain. Others said that nuts are calorie-dense and can definitely raise weight, even in moderate amounts.
So I decided to look further.
What I Found
Though I'm not a medical or dietetic professional, I do know quite a few. So I spent a substantial amount of time talking with several leading doctors and dietitians, from a variety of perspectives, to help me understand the literature and statistics in a fair and unbiased way, and had them review this article before publication. Not that they all agree about everything, but I wanted to be sure I didn't make any glaring errors here.
What I found is that there is research showing both things: a) that moderate nut consumption does cause weight gain and b) that moderate nut consumption does not cause weight gain.
Here is some of what I concluded, after reviewing a number of studies:
- Moderate intake of nuts should not cause weight gain, BUT –
- Looking at the research, “moderate intake” seems to be defined most often as about 1 ounce of nuts, two to five times a week.
- There is a very very modest cholesterol lowering effect when consuming nuts, and it mainly applies to people eating the Standard American Diet (SAD); it appears there would be little to no cholesterol-lowering effect with nuts for those following one of the healthy plant-based diets advocated by McDougall, Fuhrman, Barnard, Esselstyn, Novick, etc.
- Nutrient absorption from raw vegetables, which can be improved by nut consumption due to the fat, is largely a non-issue for people on a healthy plant-based diet; I could find nothing in the literature that suggests inadequate absorption of nutrients is a problem for those on plant-strong, starched-based, or nutritarian diets, and I could find no published evidence suggesting that not absorbing “enough” nutrients is a contributor to ill health of plant-based eaters. Getting more absorption on a poor diet may be important, but getting more on an already healthy whole food plant-based diet has no proven value.
- Nut consumption appears to be associated with longevity and with lower risk of ischemic heart disease in populations eating the SAD diet who substitute nuts in place of meat or junk food; however the diets of some of the longest-lived mostly plant-based populations, such as the Okinawans, contain only a tiny amount of nuts, and heart disease is virtually nonexistent.
- In order to show nut consumption doesn't promote weight gain, most of the published studies use calorie-restricted diets as a major feature. That is, study subjects are put on a calorie-limiting program, rather than simply adding nuts to their existing diet. (This is important because many plant-based programs are unlimited and do not require calorie counting.) When the same researchers add nuts to diets without calorie restriction, they report weight gain in subjects.
- Some major studies, which conclude that nut-eating does not promote weight gain – actually show the opposite when you look at the study data, including often-cited reviews by Loma Linda.
- Many of the studies purporting to show weight and health benefits of nuts – have been paid for by the nut industry. And despite intense Congressional lobbying and nut industry funding of a great deal of research, the FDA has graded most health claims around nuts with only a C grade, based on quality of evidence, which “represents a low level of comfort among qualified scientists that the claimed relationship is scientifically valid.” This is the same grade as the health claims made for olive oil. The exception is walnuts, which get a B.
The bottom line for me after spending time looking at numerous studies: All in all, nuts are good and have health benefits, especially walnuts. If you eat the SAD diet, you will see some modest benefits by substituting nuts for animal products or junk food. If you eat a healthy plant-based diet, then eating a few ounces a week can be healthy. But if, like AJ, you're having trouble getting to your ideal weight while otherwise eating a healthy plant-based diet, remember that those fatty little guys do pack the calories and can make it hard to lose weight.
For those who want to read and see some of what my conclusions are based on, the rest of this article contains references and discussion. I reviewed many more studies than these but I felt these tell the story pretty well, and these are some of the studies often cited by those promoting nuts.
As I said, “moderate intake” is generally defined as 1 ounce of nuts, 2 to 5 times a week. To put that in perspective, here is what a 1-ounce serving of cashews looks like:
(Photo credit: me)
That is 17 nuts. I just took that photo on my kitchen scale. So that's your day's worth – if you can stop there. Many people, probably including Chef AJ, can not.
Nuts & Weight Loss
Here is a brand new study looking at nuts and weight loss, along with a link to the full study itself:
- A randomized trial of the effects of an almond-enriched, hypocaloric diet in the treatment of obesity. Foster GD, Shantz KL, Vander Veur SS, Oliver TL, Lent MR, Virus A, Szapary PO, Rader DJ, Zemel BS, Gilden-Tsai A. Am J Clin Nutr. 2012 Jun 27. [Epub ahead of print] PMID:22743313 Free PMC Article http://www.ajcn.org/content/early/2012/06/26/ajcn.112.037895.full.pdf
This is a study where individuals were put on a calorie-restricted diet in order to lose weight. There were two groups: one ate an almond-enriched diet, the other ate a nut-free diet.
At the end of 18 months, the almond-enriched dieters lost an average of 8 pounds (3.7 kg), while those who had no nuts in their diets lost an average of 13 pounds (5.9 kg – see Table 2 of study).
So the dieters who didn't add nuts lost 62% more weight than the nut-eaters.
Interestingly, the study's authors concluded: “There were no differences in weight loss or cardiovascular disease risk factor outcomes between groups at 18 mo.”
But as you can clearly see yourself, the data shows that non-nut-eaters lost 5 pounds more the nut-eaters lost.
It's important to note that this study was paid for by the Almond Board of California and the study's principal author, Gary Foster, serves as an advisory member of the Almond Board. The study is currently being used to promote Almond sales (along with sales of other “healthy snacks” like canned tuna and low-fat milk) through press releases and “news” posts such as http://www.huffingtonpost.com/2012/07/25/almonds-healthy-weight-foods-snacks_n_1701850.html
Loma Linda University is a very vegetarian-friendly place, and has done much to advance understanding about nutrition. Here is an often-cited paper by Loma Linda researchers looking specifically at nuts and weight:
- British Journal of Nutrition (2006), 96, Suppl. 2, S79–S86 Nuts, body weight and insulin resistance. Sujatha Rajaram* and Joan Sabate´ Department of Nutrition, School of Public Health, Loma Linda University, Loma Linda, CA 92350, USA
I have put a copy of the review here:
The authors review the research on nuts and health, and the bottom line from this review appears to be that nuts cause weight gain approximately 2 pounds per year, on average.
Now interestingly this is not the authors' conclusion in the paper. But it is the conclusion you will quickly arrive at as you look at the evidence for yourself, specifically on page S81. I should say that overall this review is very good and the researchers have been careful.
But when you look at the details that the data shows, you see the following: First, the authors make the point that, in general, people who eat nuts are not heavier than other people. However, that appears to be due to the fact that people who eat nuts tend to be health-conscious in other respects, not due to anything special about nuts. This is the same phenomenon seen with dairy products. People who drink milk tend not to be heavier than other people. In fact, they are often thinner. But it is not because milk causes weight loss; it is because these are health-conscious people in many respects. We know this because, when people are fed dairy products in controlled studies, they do not lose weight at all and can easily gain weight.
The Loma Linda review shows that when researchers specifically ask people to eat nuts in controlled research studies, adding them to their existing diet, the participants tend to gain weight. This is on page S81 of the paper, linked above.
There were three studies, and in each one, the participants who were encouraged to add nuts to their routine gained weight, unless they were specifically instructed to leave out other foods to make room for the added nuts. The amount of weight gained ranged from about 1 to 2 pounds (0.4 – 1 kg) in time periods ranging from 8 weeks to 6 months. That would mean that a person who hears that nuts are healthy and starts to add them to the diet could expect weight gain of roughly 2 pounds per year, on average.
Two pounds a year doesn’t sound like much, except that, multiplied by 10 years, it starts to get more serious. Also, a 2-pound “average” weight gain means that, for every person who does not gain weight at all, someone else gains 4 pounds over a year’s time to average it out.
For one of these studies, the review summary says that men gained 0.65 kg (about 1½ pounds) over six months, while women did not gain any significant weight. However, the actual weight gain among women was 0.27 kg over six months, which is just over a half-pound in six months.
So even though the conclusion in this published review is that nuts don’t contribute to weight gain, the details in the paper show that they clearly do.
The researchers do point out that the weight gain for the nut-eaters in these studies was less than would have been predicted, given the calories in the nuts, due to several compensatory mechanisms; the calories in nuts are poorly absorbed, and people filling up on nuts are likely to compensate by leaving some other foods out, though not enough to completely prevent weight gain.
I should say the lead author of this Loma Linda review, Joan Sabate, MD, DRPH, is an advisor for the Pistachio Health Board. Not surprisingly the nut industry funds much of the research at Loma Linda on the benefits of nuts.
When you look into the “nuts do not promote weight gain” studies, you keep finding one theme, which is that nuts don't promote weight gain as long as the subjects are dieting and counting calories. Otherwise they do.
Another such study is:
- Asia Pac J Clin Nutr. 2007;16(4):588-97. A review of the evidence: nuts and body weight. Natoli S, McCoy P.
Quoting from the article:
“The findings show that the role of nut consumption in body weight management is varied. Nuts, when included as part of an energy-controlled [ie, calorie-restricted] 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.” (emphasis added)
When you hear from someone promoting nuts for weight loss, check and see if any of these studies above are nut industry ones above they are relying on. (Or post in comments below which studies they cite, and we can check them out.)
Nuts and Cholesterol
Nut consumption has been shown to have a cholesterol lowering impact in multiple studies. Just how significant is that, and how much does it apply to people who are already eating a healthy, plant-based diet?
It turns out that in the best case scenario, nuts only lower cholesterol and LDL about 6.5%. I will round that up to 7%.
This figure is from the largest meta analysis that is cited when many experts talk about this effect -- Nut consumption and blood lipid levels: a pooled analysis of 25 intervention trials. Sabaté J, Oda K, Ros E. Arch Intern Med. 2010 May 10;170(9):821-7.PMID: 20458092 http://www.ncbi.nlm.nih.gov/pubmed/20458092
A 7% reduction means that if your cholesterol is 300, the best case scenario is that by adding nuts, your cholesterol would go down to 279. Not exactly earth-shattering. Even if your cholesterol was 250, a 7% reduction would only lower it to 232, which means it would still be too high.
If your LDL is 200, a 7% reduction would bring it down to 186. If it was 150, it would lower it to only 139.5 – still too high.
Looking at the analysis, participants achieved these very modest improvements only when 20% of their total calories came from nuts, or about 400 to 450 of their calories a day (e.g., 3 ounces of cashews). A lesser amount of nuts produced less improvement.
So according to this analysis, when nuts make up 400 to 450 calories of your diet per day, you get a small benefit in cholesterol lowering – a benefit, which may be statistically significant but probably not very significant clinically.
But one of the most important points the authors of the analysis make in their article was this:
"Greater cholesterol lowering effect is found when nuts replace saturated fat than when olive oil or carbohydrates are replaced."
This means that the cholesterol improvement when you add 400 to 450 of nuts -- is going to be most significant when the nuts replace 400 to 450 calories of bacon and cheeseburgers. You won't get nearly as much of this modest cholesterol improvement if you replace 400 to 450 calories of sweet potatoes or brown rice with the nuts.
So in other words, if you already avoid meat and butter and other foods with saturated fat, and you're already eating a healthy plant-based diet, the beneficial impact of nuts to lowering your cholesterol will likely be very very small, if at all. Certainly nothing to get excited about.
The study on cholesterol and nuts was paid for by the International Tree Nut Council Research and Education Foundation, and was conducted by California Almond Board director Sabate (the same Loma Linda researcher who ran the previous nut-industry-funded study I cited which purported to show weight loss with nuts, when in fact the reverse was true). This study on cholesterol reduction is one of the most often cited by many as the basis for recommending adding nuts to lower cholesterol.
Based on a nut industry petition, the FDA allowed a “C” level qualified health claim that “scientific evidence suggests but does not prove that eating 1.5 ounces of most nuts per day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.” The FDA also insisted the label also contain a caution: “See nutrition information for fat content.”
Nuts and nutrient absorption
One thing I sometimes hear is that nuts are important because they can play a significant role for helping absorb other nutrients, especially in regard to raw veggies and salad. If you eat a poor diet, like someone who is on the Standard American Diet (SAD), and don't eat many fruits and veggies very often, getting a little additional absorption may be a good thing.
But do most of the plant-strong, starch-based or nutritarian eaters need "extra" absorption, when quality plant foods already constitute the vast majority of their calories, and greatly exceed the nutrient consumption of all the populations being studied?
I am unaware of any evidence in the literature that speaks to the question of healthy plant-based eaters significantly increasing their absorption with nuts or other fats, nor do I know of any evidence suggesting not absorbing “enough” nutrients is a contributor to ill health for plant-based eaters.
I invite anyone who knows of such studies in this area to post them in the comments below, so we can review them. If there aren't any, then the issue is just speculation. Speculation can be useful and important, but it's not science per se.
Here is a chart showing the bioavailability of carotenoids in various foods or components of foods:
You can see that raw vegetables (on the bottom) have lower absorption than fruits and starches (toward the top).
In any case, it's well known you can increase absorption by simply cooking and/or chopping up raw foods before eating.
Any healthy plant-based diet from any of the leading experts – Ornish, Fuhrman, McDougall, Barnard, Esselstyn -- already far exceeds the amounts of all recommended carotenoids and other nutrients. All of these diets are way more nutrient dense than the healthiest diet any of the subjects in any of these studies is consuming, and already providing 30 to 90 times the amounts of various nutrients shown to be of benefit in several of these studies.
And I don't know of any studies suggesting that the many – probably millions – of people with nut allergies have nutrient absorption problems which lead to medical problems.
The Okinawans get less than 1% of their calories from nuts, which is about one ounce (or 17 cashews total) every two weeks. That is well below nut industry-funded study recommendations. Yet the Okinawans are some of the longest lived people on the planet.
The nut-funded research of the Adventist Health Study are done on vegetarians and vegans, and suggest the more nuts people eat, the healthier they are. But the healthiest diets of the Adventist people, while clearly healthier than the Nurses Health Study group, are nowhere near as healthy as the diets recommended by Fuhrman, Barnard, McDougall and Esselstyn.
Most importantly, in the same Adventist Health Study data suggesting that greater nut consumption equates with greater longevity, we see that the fruitarians eat more nuts than the vegans, who eat more nuts than the vegetarians, who eat more nuts than the meat-eaters: (click first image to enlarge)
So it's very clear that nut consumption is probably just a marker for an otherwise healthy diet, in the same way that nuts appear to be a marker in the Nurses Health Study for women with a healthier diet, lower body weight, who don't smoke and exercise more often. The data could simply be indicating: go vegetarian to become healthier, vegan to become healthier than that, or raw to become even more healthy, rather than claiming that it's just because of nut consumption. Obviously the overall picture of what the vegetarians, vegans and fruitarians were eating is far more important in explaining their superior health, than saying it's all due to nuts (and then trying to use this to sell nuts to people eating an otherwise bad diet).
Diabetes and Nuts
Research from the Nurses Health Study also shows that consuming as little as 2 ounces of nuts per week (not per day) was beneficial to participants in regard to heart disease. (Again, 2 ounces per week is not that much nuts, and more than many are eating.)
Now if you eat a largely unhealthy SAD diet, like most in the Nurses Health Study, perhaps you could see benefit by adding 2 ounces a week of nuts – if you consumed those nuts in place of roast beef, cheeseburgers, or processed junk food.
The Nurses Health Study also showed that women who ate 1 oz of nuts 5 or more times a week had a lower risk of diabetes. The review is called:
- Nuts as a Replacement for Carbohydrates in the Diabetic Diet. JJAMA, 2002 Nov 27; 288:2554-2560. Rui Jiang, MD; JoAnn E. Manson, MD; Meir J. Stampfer, MD; Simin Liu, MD; Walter C. Willett, MD, DrPH; Frank B. Hu, MD, PhD
The data shows these women were also less likely to smoke, more likely to exercise and had a higher dietary fiber intake, all of which we know are also protective against diabetes.
Perhaps most importantly, the authors recommend that you substitute reasonable portions of nuts for refined grain products, meat or processed foods – but that you do not simply add nuts to your present diet. Here is their conclusion from the study:
“Our findings suggest potential benefits of higher nut and peanut butter consumption in lowering risk of type 2 diabetes in women. To avoid increasing caloric intake, regular nut consumption can be recommended as a replacement for consumption of refined grain products or red or processed meats.” (emphasis added)
Another study looked at replacing unhealthy carbohydrates with nuts, to see what the impact would be for diabetes. The study is:
- Nuts as a Replacement for Carbohydrates in the Diabetic Diet, Diabetes Care 34:1706–1711, 2011 http://care.diabetesjournals.org/content/34/8/1706.full
In this study, subjects received either a muffin or 2 oz of nuts. Those who received the nuts were said to have “improved glycemic control.” However, when we look closer at the numbers what we find is their glucose only went from 132 to 130 and their HbA1c only dropped from 7.1 to 6.9 and leveled off after the 8th week with no further improvement. Normal blood sugar is under 100 and normal HbA1c is under 5.5. So as we can see, both of these numbers are still fairly high, and the improvements were minimal at best – and were only seen when compared to those getting a muffin, which by the way was made with apple concentrate, egg whites and skim milk powder. Hardly a health food.
Here are three other randomized controlled studies of nuts and diabetes:
- Diabetes Care. 2010 Feb;33(2):227-32. Epub 2009 Oct 30. Effects of walnut consumption on endothelial function in type 2 diabetic subjects: a randomized controlled crossover trial.
This study found that "The walnut-enriched diet increased fasting serum glucose" i.e., blood sugar. Ooops! Not good for diabetics.
- Am J Clin Nutr. 2002 Nov;76(5):1000-6. Effect of diets enriched in almonds on insulin action and serum lipids in adults with normal glucose tolerance or type 2 diabetes.
This study concluded: "Almond-enriched diets do not alter insulin sensitivity in healthy adults or glycemia in patients with diabetes."
- Diabetes Care. 2004 Dec;27(12):2777-83. Including walnuts in a low-fat/modified-fat diet improves HDL cholesterol-to-total cholesterol ratios in patients with type 2 diabetes.
This study found that: "There were no significant differences between groups for changes in body weight, percent body fat, total antioxidant capacity, or HbA1c levels."
So for the one study that says nuts are better than a muffin made with eggs and milk, those are three studies that show nuts don't help diabetes at all, or may make blood sugar worse.
If you already eat a healthy low-fat plant-based diet (like probably no one in any of these studies did), and you aren't eating red or processed meat, or refined grains (junk food), then this information is pretty meaningless to you. And if you're still eating bacon, well don't just add some nuts to your diet that won't do much if anything -- become a healthy plant-based eater instead, and get some real benefits!
The same research that says nuts are health food says oily salad dressing is health food
Remember that the Nurses Health Study – where too much of this comes from – is an observational study. It's not a study on nuts.
The truth is dietary patterns matter much more than any one food, good or bad. Taking isolated information based on an isolated aspect of an isolated food...is not very useful at all in the big picture, when there is no context or perspective. Major scientific bodies agree.
I see too often in the veg health community people being told to they really must tweak their diets this way or that, or worry about this food or that – based on research conducted on people eating the awful Western diet. We all know the scientific literature abounds with studies showing olive oil and the Mediterranean diet have big benefits. In fact, all the same data from the Nurses Health Study, cited to promote nuts, also shows that olive oil is healthy and protects against fatal ischemic heart disease.
The Nurses Health Study began in 1976 and has grown over the years. In 1984 a group of about 80,000 women filled out a 116-item food-frequency questionnaire. Researchers then looked 10 years later, saw how many had died and of what diseases, and what the health was of others still alive, and began drawing conclusions from the self-reported questionnaire data. What did they say they were eating in 1984? What did some of them die of? Who is still alive and healthy? Do we see patterns?
The same data from the Nurses Study which says nuts can help prevent heart disease also says oil will do the same thing. The Nurses Health Study has been used to suggest higher consumption of oil-based salad dressings to reduce the risk of fatal ischemic heart disease, see: http://www.ncbi.nlm.nih.gov/pubmed/10232627
Well no credible plant-based health professional I know is recommending adding oil – or any other processed foods – in order to prevent heart disease. All of these programs seek to limit or eliminate oil. It's well known that even olive oil consumption impairs endothelial function, and a lot has been published to show this (not funded by the food industry), e.g. see
http://www.ncbi.nlm.nih.gov/pubmed/11079642 A meal enriched with olive oil impairs flow medial dilation (blood flow) by a whopping 31%, similar to the effect of eating a Big Mac.
While plant-based experts with clinical experience do not recommend oil to “fight heart disease,” data from the Nurses Health Study says peanut butter and oily salad dressings are health foods that can do just that. In truth, substituting olive oil for other saturated fats like butter IS an improvement on an otherwise unhealthy diet. And for people eating an awful diet, they may see some small improvement by switching from butter to olive oil. But adding oil into a healthy plant-based diet is obviously not an improvement.
The Nurses Health Study is silent on how to improve healthy plant-based diets. Attempting to use this research to do so is at best a guess.
It's interesting to note that Dan Buettner, author of Blues Zones, which examines research on factors for longevity, cites nuts as one of the factors for long life – though not all the long lived populations include them. Buettner also cites drinking alcohol, eating olive oil, and believing in God as longevity factors. Well there is a lot of booze, oil, and prayer in Mississippi, so shouldn't it be a pretty healthy place?
And of course the Adventist population doesn't drink alcohol – one of the "keys to longevity" – and yet they're still among the long lived populations, just like the Okinawans who eat very few nuts.
You can see the profound problems of using population studies to try to make guidelines focusing on one aspect or one food or one disease.
Buying health claims
Industry spends a lot of money trying to produce studies that make their products look as healthy as possible, so that they can assert health claims to help sales. The FDA reviews and “grades” the research involved when determining whether to let the claims be made. The research for nuts gets a “C” grade (level 3) ranking, meaning that the evidence for nuts for weight loss and heart health reflects a “low level of comfort among qualified scientists that the claimed relationship is scientifically valid,” and that the scientists have “a low degree of confidence that results [of studies backing the claims] could be extrapolated to the target population.”
On the other hand, the evidence that a diet heavy in fruits, veggies and whole grains produce many health benefits gets an A rating, the “highest rank of scientific evidence to support the substance/disease relationship meets the 'Significant Scientific Agreement among qualified experts' standard...reflects a high level of comfort among qualified scientists that the claimed substance/disease relationship is scientifically valid.”
Nuts and weight loss: My conclusion
All in all, nuts are good and have health benefits, they certainly are not poisons. If you eat the SAD Western Diet, research “suggests but does not prove” that eating nuts as a replacement for meat and junk food can have some benefit.
If you're eating a whole food plant-based diet, eating a few ounces a week can also be healthy.
If you're eating a healthy plant-based diet including nuts, and can't seem to lose the weight you want, I would recommend following the research that shows nuts will put on weight, and lose the nuts.