Scientists talked about the effect of nuts on body weight

Nuts are often excluded from the diet when trying to lose weight due to their high calorie and fat content. However, their energy value does not necessarily mean an increase in body weight: a large analysis of clinical studies showed that regular consumption of these products did not lead to significant weight gain. Moreover, scientists have found small changes in body composition and levels of some blood parameters. About why high—calorie nuts do not necessarily interfere with weight control, see the Izvestia article.

Calories are not equal to kilograms

The results of a systematic review and meta-analysis are published in the journal Foods. The researchers reviewed 154 scientific publications, which presented 119 randomized controlled trials. The quantitative meta-analysis included data from 102 papers. The median follow-up period was 21 weeks.

The research involved adults who consumed whole tree nuts and peanuts. Scientists compared their diets with various food options, from the usual menu to calorie—restricted diets. Nuts with different ratios of monounsaturated and polyunsaturated fatty acids were considered separately.

On average, eating nuts was accompanied by an increase in energy intake of about 120 kcal per day. Nevertheless, no significant changes in body weight, body mass index, and waist circumference were found in the overall sample. In other words, the participants did not gain weight, despite the fact that, according to the reports, they received more calories from food.

Scientists talked about the connection of walnuts with improved mood

There is less adipose tissue

At the same time, the analysis showed small changes in body composition. On average, the proportion of adipose tissue decreased by about 0.3 percentage points, and its absolute weight decreased by about 0.41 kg. The proportion of fat-free weight, on the contrary, increased by 0.71 percentage points. However, the absolute mass of fat-free tissue has not changed significantly. Therefore, the results do not allow us to say that the participants gained muscle: we are talking about a change in the ratio of fat and non-fat tissue in the body.

The researchers also compared different types of nuts. In the group of products with a predominance of monounsaturated fatty acids, a decrease in fat mass of about 0.42 kg was recorded. However, there were no statistically significant differences between the groups of nuts with different fatty acid composition in terms of the main body composition indicators. Therefore, the work does not prove that one type of nuts is more effective than another for weight control.

What happens to cholesterol

The authors of the review also assessed changes in blood lipid profile parameters. Eating nuts was associated with a slight decrease in total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides. At the same time, the researchers did not find a significant effect on the level of high-density lipoprotein (HDL) cholesterol.

A decrease in total cholesterol and LDL was observed when eating nuts of both studied categories. A decrease in triglyceride levels was recorded in the group of nuts rich in monounsaturated fatty acids. However, the authors assessed the confidence in these results as very low, so it is not yet possible to draw unambiguous conclusions about the advantage of such a composition.

Researchers have suggested that unsaturated fatty acids may affect the production of cholesterol in the body and its removal from the blood. Possible effects on triglyceride metabolism are also considered as one of the explanations. But these mechanisms were not tested directly in the meta-analysis.

Why conclusions are still cautious

Scientists have considered several possible explanations for why the extra energy from nuts was not accompanied by the expected increase in body weight. In particular, dietary fiber, protein, and fats can affect satiety and appetite, and some of the fats from whole nuts may not be fully absorbed. However, the new review did not establish which mechanism explains the results.

In addition, there were too few studies on appetite and energy expenditure for a full-fledged meta-analysis. Their results were heterogeneous: in some studies, participants reported a decrease in hunger or increased satiety, while in others such changes were not observed.

The authors also noted differences between the included studies: they used different methods to assess body composition, and the duration of follow-up and the diets of the participants did not match. Confidence in the evidence varied depending on the indicator: for changes in the proportion of adipose tissue, it was moderate, and for some other results, including waist circumference and triglyceride levels, it was very low.

Thus, the meta-analysis did not confirm the concern that eating nuts by itself necessarily leads to weight gain. But the changes found were small, and the study did not assess the long-term health effects. Therefore, the authors do not claim that the amount of nuts in the diet does not matter.