Nuts and Bodyweight – Q&A

Question: I have a follow-up to the article you posted on Monday regarding 10 Tips to Deal with Holiday Weight Gain. A lot of parties I attend during the holidays have various sorts of nuts as snacks and my question is how they impact on body weight. I have read that they are healthy but they also seem to contain a lot of calories, what’s the deal with them? Thank you.

Answer: Nuts are sort of strange nutritionally. On the one hand they are generally very nutritious, they provide a decent amount of quality protein and, although sometimes high in fat, the fats they contain are generally of the healthy kind, nuts are generally high in fiber as well. Nuts are also a good source of magnesium, Vitamin E and research indicates that they may contain important phyto-chemical compounds beneficial to human health; diets containing nuts have also been shown to improve blood lipid profiles.

On the other hand, they can be extremely nutritionally dense (that is, providing a lot of calories in a very low volume). This gives them the potential to negatively affect body weight.

However, a fairly large body of research indicates that nuts don’t seem to impact body weight negatively, at all. That is, various research studies have provided some amount of nuts in addition to the normal diet to see what happens to body weight. In general, the addition of nuts has had limited or no impact on body weight. Phrased differently, despite the addition of calories from nuts, weight doesn’t change/isn’t affected. What’s going on?

Research has identified three possible mechanisms to account for the observed results.

Satiety: Nuts appear to increase fullness and calories from nuts seem to be compensated later in the day. That is, it’s suggested that the calories from nut intake results in a spontaneous decrease in food intake later in the day such that total energy balance is unchanged.

One type of study, called a preload study has examined this, providing a fixed number of calories from nuts and then seeing what happens to spontaneous food intake at a buffet type meal later on. Invariably, nut intake (one study tested almonds, chestnuts, and peanuts) causes people to eat less at the buffet meal

However, despite the impact of nuts on fullness, this still isn’t sufficient to account for the lack of an impact on body weight from nut consumption and other mechanisms must be at work.

Increased Energy Expenditure: Some work has identified an increase in energy expenditure due to nut intake; some research has found an increase in resting energy expenditure with chronic nut intake as well. This could be due to the protein content (protein has the largest effect on TEF for example), the fatty acid profile, or both.

Increased Fecal Energy Loss: With nut consumption, there is increased energy loss in your poop, that is, some proportion (one study found a 7% increase) of ingested calories are excreted without absorption. This is likely due to the fiber content of the nuts or some other compound that limits digestive/absorption capacity for nuts.

The three factors above have been shown to account for 95% of the total energy value of the nuts so there is still a small amount unaccounted for. In any case, nuts, despite their high energy content, simply don’t seem to have the negative impact on body weight that one might expect. Which, mind you, doesn’t mean that you can eat them with no attention to portions or intake of other food, recall that a big part of the above effect is due to caloric compensation. If you’re adding a ton of calories from nuts and don’t end up reducing your intake from other sources, the potential for fat/weight gain certainly is there.

Which is basically a long way of saying to eat them, just not without paying some attention to overall intake.

Reference:

Mattes, RD. The Energetics of Nut Consumption. Asia Pac J Clin Nutr (2008) 17 (S1): 337-339.