Swapping serving of meat or starch with nuts linked to less weight gain 12/06/2018
Nuts are fatty, so they must be fattening, right?
One gram of fat contains a little over twice as many calories (9) as the same amount of protein or carbs (4).
And although nuts get most of their calories from fat, they seem to exert benign effects on weight and body composition — ones that defy expectations.
Beyond their well-known cardiovascular benefits, recent studies suggest that nuts may help prevent weight gain and bring other metabolic benefits. (See Studies Confirm Popular Nuts as Conspicuously Healthful, in which we summarized research published through 2006.)
Five years ago, Spanish researchers published a meta-analysis of 33 clinical trials and came to this conclusion: “Compared with control diets, diets enriched with nuts did not increase body weight, body mass index, or waist circumference in controlled clinical trials.” (Flores-Mateo G et al. 2013)
Before we examine the results of four recent studies that support their conclusion, let’s quickly review the nature of nuts.
Nuts reduce heart and death risks
The American Heart Association has long recommended eating a daily serving of nuts, which is small handful of — about 1.5 ounces — of whole nuts or two tablespoons of nut butter.
That recommendation is based on ample epidemiological evidence linking nutty diets to reduced risks for death from cardiovascular disease or any other chronic disease.
For example, a joint US-Chinese team analyzed health and diet data from 206,029 American (white and black) and Chinese people and found that those who ate the most nuts had the lowest risk of death from any cause, including cardiovascular disease. As they wrote, “Consumption of nuts … may be considered a cost-effective measure to improve cardiovascular health.” (Luu HN et al. 2015)
And at least seven other recent epidemiological studies linked nutty diets to reduced risk of death from any cause — one of which (Bao Y et al. 2013) we covered in Nuts for Longevity?.
For more reports on research in this realm, see the Nuts, Seeds, & Grains section of our news archive, and search our website for “nuts”.
In addition to polyunsaturated fat — mostly the omega-6 type — popular nuts such as almonds, hazelnuts, Brazil nuts, peanuts, pecans, pistachios, and (especially) walnuts deliver substantial amounts of protein, fiber, antioxidants, vitamins, and minerals.
Nuts appear very healthful, even though they're high in omega-6 fats and low (except walnuts) in omega-3 fats. For more on that, see "Nuts are healthful, despite high omega-6 levels", below.
This chart shows the nutrient composition* of one-ounce servings of popular nuts (except peanuts). The red numbers indicate the highest values for each nutrient:
*U.S. Department of Agriculture, Agricultural Research Service. 2010. USDA National Nutrient Database for Standard Reference, Release 23.
Now, let's look at four recent studies whose results support the idea that nuts can help prevent weight gain — without causing blood-sugar problems.
California studies support nuts’ anti-obesity power
The Loma Linda University School of Public Health (LLUSPH) is surrounded by nut farms and known for its many nuts-and-health studies — ones typically funded by nut trade associations.
That corporate funding — and the University’s religiously inspired vegetarian orientation — invites caution about this research. (LLU is owned and run by the Seventh-day Adventist Church.)
But — like the two LLU studies described below, which involved other institutions — most epidemiological studies worldwide, regardless of their funding, link nutty diets to better health.
California Study #1 — Nutty diets reduced weight gain
For this study, researchers from Loma Linda joined colleagues from California’s International Agency for Research on Cancer to analyze medical, bodyweight, diet, and lifestyle data provided by 373,293 adults from 10 European countries, who’d participated in the EPIC-PANACEA study, designed to look for obesity risk factors. (Freisling H et al. 2018)
Over the course of the five-year study, the Europeans who reported eating the most nuts — peanuts, almonds, hazelnuts, pistachios, and/or walnuts — gained less weight and were less likely to become overweight or obese.
It’s worth noting that a separate EPIC study linked nuttier diets to healthier aging and memory function in seniors – possibly due to the high levels of antioxidants and essential nutrients in nuts, and their generally healthy nature compared with processed snack foods.
Senior investigator Joan Sabaté, MD, DrPH of LLUSPH said their findings contradict conventional advice to avoid nuts because — by comparison with vegetables, grains, and lean meat or fish — they’re high in fat and calories.
As Dr. Sabaté said in a press release, “To me, this confirms that nuts are not an obesogenic food.”
But that’s only true if you eat nuts in place of other foods, instead of adding them to a diet that provides enough calories to meet your individual needs.
California Study #2 — Walnuts didn’t raise body weight or body fat
Researchers from LLU conducted a randomized clinical trial designed to examine the effects of habitual walnut consumption on body weight and body fat in older people.
The trial — called the Walnuts and Healthy Aging study — lasted two years and included 356 men and women (average age 69 years; 67% women).
The participants were randomly assigned to one of two groups:
- Control group: Ate no walnuts during the trial.
- Walnut group: 1 to 2 ounces of walnuts daily. Each participant received a customized amount that would provide about 15% of their daily calorie requirements, based on weight, height, and other factors.
Each participant’s weight and body fat composition was measured periodically, and that data was adjusted to account for any self-reported changes in physical activity during the trial period.
After two years the participants average body weight dropped significantly, while their proportion of body fat rose significantly.
However, there were no significant weight or body-fat differences between the control and walnut groups.
In addition, the participants in both groups experienced very little change in their lean body mass (muscle), waist circumference, or waist-to-hip ratio.
As the LLU researchers concluded, “Our findings indicate that walnuts can be incorporated into the daily diet of healthy elders without concern for adverse effects on body weight or body composition (Bitok E et al. 2018).
In other words — even though the participants weren’t asked to cut back on other foods — eating amounts of walnuts equal to 15% of each volunteer’s daily calorie requirements didn’t adversely affect their weight, body fat, muscle mass, or body shape.
American Heart Association presents two other supportive studies
Two studies presented last month at the American Heart Association (AHA) Scientific Sessions 2018 conference in Chicago lend further support to the anti-obesity potential of a daily nut habit.
AHA Study #1 – Substituting nuts for red meat, starch, or sugar
This analysis of prior epidemiological studies came from the Harvard School of Public Health, and was led by Xiaoran Liu, Ph.D.
She noted that small changes to diet can have big impacts over time: “Once people reach adulthood, they start to gradually gain about one pound a year of weight, which seems small. But if you consider gaining one pound over 20 years, it accumulates to a lot of weight gain.”
And she described the gap between perception and reality: “People often see nuts as food items high in fat and calories, so they hesitate to consider them as healthy snacks, but they are in fact associated with less weight gain and wellness.”
Her team analyzed the answers to diet surveys provided every four years by 126,190 health care professionals enrolled in three famed studies: 25,394 men in the Health Professionals Follow-up Study, 53,541 women in the Nurse's Health Study and 47,255 women in the Nurse's Health Study II.
The results of the Harvard team’s analysis found a lower risk of weight gain and obesity among the participants who reported eating a one-ounce serving of tree nuts or peanuts daily, in place of a corresponding amount of calories from red meat, processed meat, French fries, or sugary snacks.
As Dr. Liu said, “Adding one ounce of nuts to your diet in place of less healthy foods … may help prevent that slow, gradual weight gain after you enter adulthood and reduce the risk of obesity-related cardiovascular diseases.”
Although epidemiological studies often link above-average consumption of red meat with greater health risks, the unhealthful habits associated with that dietary habit — low exercise levels, smoking, and eating a broadly unhealthful diet — undermine confidence in those links.
And the diets and lifestyles of people who choose grass-fed meats are generally more healthful than average, since they include more exercise and fresh produce and fewer starchy or fried food and sugars.
AHA Study #2 — Brazil nuts aid blood sugar health
In this study, San Diego State University scientists examined the effects of Brazil nuts on feelings of satisfaction and on insulin and blood sugar levels — versus pretzels.
For their clinical study, the researchers recruited 22 adults with an average body mass index (BMI) in the center of the normal range (22.3).
The volunteers were divided into two groups, assigned to eat either pretzels or Brazil nuts — providing equal amounts of calories and sodium — in addition to their usual diet:
• Pretzel group: 36 grams of pretzels
• Brazil nut group: 20 grams of nuts (about five nuts).
These amounts resulted in a similar addition of calories and sodium to the participants’ diets.
While both the nuts and the pretzels made participants feel comparably full and hunger-satisfied, those benefits were greater in the Brazil nut group.
And while pretzels prompted significant spikes in blood sugar and insulin 40-minutes after they were eaten, Brazil nuts didn’t significantly raise either risk factor for diabetes and cardiovascular disease.
It’s really no surprise that pretzels worsened those specific metabolic-health risks compared with Brazil nuts.
But — in addition to being lower-carb and rich in beneficial nutrients — why would eating the same number of calories from Brazil nuts have so little negative effect versus the pretzels?
One answer could be the high levels of selenium — an element essential to the body’s own antioxidant network — in Brazil nuts.
Clinical studies from New Zealand and Brazil found that eating small amounts of Brazil nuts daily raised people’s selenium levels dramatically, and significantly raised their levels of a key internal antioxidant enzyme called glutathione peroxidase (Thomson CD et al. 2008; Cominetti C et al. 2011).
However, Brazil nuts are not just selenium-delivery systems, and recent clinical studies that examined the effects of supplemental or food-borne (i.e., from mushrooms) selenium found that it worsened some aspects of blood sugar control and improved others (Pounis G et al. 2013; Faghihi T et al. 2014; Asemi Z et al. 2015; Jablonska E et al. 2016).
Nuts are healthful, despite high omega-6 levels
Scientists familiar with the relevant research decry the huge, historically unprecedented amounts of omega-6 fatty acids in the standard American diet — which come mostly from cheap vegetable oils: corn, soy, cottonseed, safflower, and sunflower.
The exceptions are oils containing at least 70% oleic acid, for which the FDA just approved a cardiac health claim based on this agency finding: "Oleic acid is a monounsaturated fat which, when substituted for fats and oils higher in saturated fat, may reduce the risk of coronary heart disease."
Accordingly, it’s best to cook with olive oil (always choose antioxidant-rich extra virgin grade), macadamia nut oil, non-GMO canola oil, and "high-oleic" versions of sunflower oil — which are low in omega-6 fatty acids.
However, nuts are healthful — especially if you’re not also consuming lots of the cheap, omega-6-rich vegetable oils that predominate in most packaged, restaurant, and take-out foods.
Walnuts are the only nuts with significant amounts of omega-3 fatty acids — albeit the “short-chain” plant-food form known as ALA, which is much less beneficial than the “long-chain” omega-3s (DHA and EPA) found in seafood — especially fatty fish such as sardines and salmon.
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- American Heart Association Scientific Sessions 2018. Presentation Sa1297, Session LF.APS.02. November 10, 2018.
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