The calorie principle has been a central theme in weight loss advice for some decades, and encourages individuals keen to lose weight or maintain their weight to avoid calorific foods. However, for a variety of reasons, calorific foods may not be fattening, and in fact might even promote weight loss. Some of the most important mechanisms at play here were explored in a study which I reported on in October, which specifically examined the relationship between nut eating and weight.
In summary, this study found that nuts are not, generally speaking, at all fattening. And this appears to have to do with the following major factors:
1. Nuts tend to satisfy the appetite
2. Nuts have relatively low glycaemic index, and therefore tend not to stimulate much in the way of secretion of insulin (the chief fat storage hormone)
3. Nuts stimulate the metabolism
4. Not all of the fat in nuts is absorbed from the gut
Support for the idea that nuts are not fattening has come from a study that is currently in press at the American Journal of Clinical Nutrition [1]. This study of over 50,000 women over an 8-year period found that eating more nuts was not associated with weight gain. In fact, women eating nuts two or more times each week tended to put on less weight and be less prone to obesity compared to those who rarely ate them. One explanation here, of course, is that women less prone to weight gain are perhaps less likely to feel restrained regarding their intake of ‘fattening’ foods such as nuts. However, because of the mechanisms listed above, there is reason to believe that nut-eating might genuinely promote weight maintenance or even weight loss.
One way to test this theory is to actually feed people nuts to see what effect this has on their weight. This was done recently in a study published in the Scandinavian Journal of Clinical and Laboratory Investigations [2]. In this study, adults were fed with peanuts in addition to their normal diet at a ‘dose’ of 20 calories of peanuts per Kg of body weight per day. (Peanuts are not, strictly speaking, a nut. They are legumes, but have a nutritional make-up akin to tree nuts). That’s a lot of additional calories. However, despite this, after two weeks, weight had not increased significantly. Waist circumference did not increase either. Metabolic rate, however, saw a significant rise.
Now, while this group were munching on peanuts, another group was adding a similar number of calories into their diets in the form of candy (high sugar snacks). Yet the results were quite different: both weight and waist circumference increased significantly. Metabolic rate did not rise, but levels of supposedly unhealthy LDL cholesterol did.
While the number of individuals in this study was small and the study duration was short, what we clearly have here is two very different results from the addition of the same amout of two very different foods. It provides, yet more evidence, to support the idea that a calorie is not a calorie.
References:
1. Bes-Rastrollo M, et al. Prospective study of nut consumption, long-term weight change, and obesity risk in women. Am J Clin Nutr (April 29, 2009).
2. Claesson AL, et al. Two weeks of overfeeding with candy, but not peanuts, increases insulin levels and body weight. Scand J Clin Lab Invest. 24th April 2009 [epub ahead of print]
