A word from: Edith Feskens - Wageningen University, Division of Human Nutrition

Expert opinion on GI and nuts

Coming from the world of diabetes research, my appraisal of nuts in foods was in the past rather mixed. Until the eighties it was assumed that diabetic patients, both the Type 1, or insulin-dependent, and Type 2 or non-insulin-dependent, were best off with a diet limited in carbohydrates. At that time it became clear that the dietary guidelines for diabetic patients should focus on limiting the rate of occurrence of cardiovascular diseases. Thus, it made sense to change the diet in order to reduce blood pressure and LDL cholesterol. At that time however, nuts were regarded as containing too much fat and too much salt.

However, very interesting data was reported in the Journal of the American Medical Association (JAMA) in 2002. A renowned group of researchers from Harvard University reported on the results from a cohort of women, ± 84,000 subjects whose eating patterns had been followed for 16 years. The frequency of nut consumption appeared to be inversely related to the development of Type 2 diabetes: women that consumed one serving of nuts at least five times or more per week had a 27% lower risk diabetes. Also the use of peanut butter was inversely related to diabetes, and these results were adjusted for all kinds of so-called confounding factors, so that they could not be related to other characteristics of the nuts eaten by peanut butter users. The authors gave several potential explanations for their findings: nuts contain polyunsaturated fatty acids, which are known to affect insulin resistance beneficially, the underlying metabolic cause of Type 2 diabetes. Magnesium and dietary fibre were also mentioned as being beneficial components.

Later, the GI, or glyceamic index, was also suggested as playing a role. This is a very interesting topic: carbohydrates are known to elicit different glucose and insulin spikes in the blood, and hence affect blood glucose control in diabetic patients (proven), play a role in the prevention of Type 2 diabetes (possible) and obesity by, inter alia, increasing satiety (some evidence available).

In general, nuts do indeed have a low GI. However, limited information is available about the specific GI values of nuts. The content of carbohydrates in nuts is low, and it is therefore unlikely that the GI of nuts is an important factor in blood glucose control, satiety or body weight control. However, the observation from Harvard remains interesting!

Nuts and health – Special: Peanuts and nuts and body weight

The benefits of peanuts and nuts on body weight

The general conviction is that the consumption of tree nuts and peanuts leads to weight gain. This conviction is based on the fact that peanuts and nuts are high-energy dense foods (> 4 kcal/g). However, results of recent studies indicate either a positive effect or no relationship between peanuts and nuts consumption and weight maintenance. One of the mechanisms behind the inverse relationship between peanuts and nuts and weight gain is their positive effect on satiety. In this newsletter, About Nuts presents an update of the scientific evidence.

Satiety

Satiety is the condition of feeling full or gratified beyond the point of satisfaction. It helps to prevent overeating and therefore weight gain. Various studies indicate that peanuts and nuts have a strong satiating effect.^1,2 This is the result of their nutritional composition: high protein (± 16 g/100g), high fibre (± 5 g/100g) and a high energy content (> 4 kcal/g). Among the three macronutrients, proteins have the greatest satiating effect. Fibres promote a sense of satiety by slowing the rate at which foods leave the stomach. Also, the large amount of energy reduces the feeling of hunger.

Glyceamic Index

Peanuts and nuts have a low glyceamic index (GI). The GI is a system of ranking carbohydrates in foods on a scale from 0 to 100, according to the extent to which they raise blood glucose levels after eating. High GI foods result in a swift increase in blood sugar levels, while low GI foods result in a gradual increase. Food products with a GI value of less then 55 are considered as low GI foods. Low GI diets have benefits for weight control because they help to control appetite and delay the feeling of hunger. Peanuts and nuts contain a low amount of carbohydrates, which results in GI values of between 7 and 25. Despite the positive effect of low GI foods on satiety, it is thought that the positive effect of peanuts and nuts on body weight is due to other mechanisms.³

Body weight

Various studies indicate that incorporating peanuts and nuts in a regular diet does not lead to weight gain.^4,5,8 Three recent reviews by St-Onge,⁴ Garcia⁶ and Coates⁷ even indicate that there is support for a certain role of peanuts and nuts in the maintenance of a healthy weight. Brufau et al.³ suggest in their review that their effect on body weight can be explained by several factors. Firstly, the absorption of energy from peanuts and nuts seems to be incomplete. This results in an incomplete release of fatty acids during digestion. Secondly, because of the satiating effect of fibre, which decreases energy intake. And thirdly, owing to the increase in resting energy expenditure and diet-induced thermogenesis, which may result in reduced fat storage. No consensus has yet been reached on the exact role of peanuts and nuts, partly owing to the lack of long-term, extensive studies. However, there are strong indications that the consumption of peanuts and nuts has a positive effect on body weight.

Conclusion

Despite the high energy content of peanuts and nuts, they do not seem to cause an increase in body weight when incorporating one hand of peanuts or nuts (30 gram) in a daily diet. They may even have a positive effect on body weight control. There are several components in peanuts and nuts that can play a role in the observed effect. However, it is yet unclear which nutrients or mechanisms are responsible.

References
1) Salmeron J, Manson JE, Stampfer MJ, Colditz GA, Wing AL, Willett WC. Dietary fibre, glycaemic load, and risk of non-insulin-dependent diabetes mellitus in women. Journal of the American Medical Association 1997a; 277:472-477.
2) G. Brufau et al. Nuts: source of energy and macronutrients. Spain. British Journal of Nutrition, 96, supplement 2, S24-S28, 2006.
3) Josse AR, Kindall CWC, Augustin LSA, Ellis PR, Jenkins DJA. Almonds and postprandial glycemia-a dose-response study. Metabolism 2007; 56:400-4.
4) St-Onge MP. Dietary fats, teas, dairy and nuts: potential functional foods for weight control. AM J Clin Nutr 2005; 81: 7-15.
5) Kirkmeyer SV, Mattes RD. Effects of food attributes on hunger and food intake. Int J Obes Relat Metab Disord 2000; 24: 1167-75.
6) Gracia-Lorda P, Rangil IM , Salas-Salvadó J. Nuts consumption, body weight, and insulin resistance. Eur J Clin Nutr 2003; 57: S8-11.
7) Coates AM, Howe PRC. Edible nuts and metabolic health. Current opinion in lipidology 2007; 18:25-30.
8) Nes-Rastrollo M, et al. Nut consumption and weight gain in a Mediterranean cohort: the SUN study. Obesity. 2007; 15: 1.