1. A word from PD Dr. Achim Bub, Max Rubner-Institut Germany

„Nuts are fattening foods”: this is history. For a long time the high fat content of nuts raised concerns about their nutritional value. Now it seems clear that nuts can substantially contribute to a healthy diet. The advice for regular nut consumption has been included in nutritional recommendations, for example in Germany and the US (German Nutrition Society, American Heart Association). Moreover, this issue is supported by a qualified health claim linking nut consumption with reductions in the risk of cardiovascular disease. In their recent review Rajaram & Sabaté conclude that no increase in body weight occurs when nuts are incorporated in the daily diet. These findings are based on results from epidemiological, metabolic and free-living studies. However, some questions from controlled metabolic studies remain. A calculated positive energy balance has been demonstrated in such human feeding trials and the authors discussed the following issues contributing to this observation: insufficient fat absorption, impact on satiety, postprandial thermogenesis, fatty acid oxidation or an increased resting metabolic rate. Scientists from Purdue University, West Lafayette, now report in the American Journal of Clinical Nutrition on the role of almond mastication on lipid bioaccessibility, appetite and hormone response. In a randomized crossover study, 13 healthy adults were advised to chew 55g almonds 10, 25, or 40 times, respectively. Appetite was monitored and postprandial gastrointestinal hormone response was investigated. The authors found that hunger was suppressed below and fullness elevated above baseline when chewing almonds 40 times compared to 25 times. This was accompanied by an elevation of the satiety mediating gut hormone GLP-1 (glucagon-like peptide-1) in blood, which could explain the satiating effect of chewing almonds 40 times. Furthermore, this study showed higher faecal fat excretion and energy loss after 10 chews compared to 25 or 40 chews. The study demonstrates well the importance of chewing on the fat and energy accessibility from nuts, and the final impact on satiety sensations in humans. Whether this contributes to body weight regulation needs to be investigated in controlled long-term human intervention studies. However, at least some of the above-mentioned questions related to the positive energy balance in controlled human nut feeding trials could be answered. Considering the low fat and energy absorption simply from chewed nuts one should not forget that this goes along with lower availability of favourable unsaturated fatty acids, phytosterols, vitamins, and antioxidants such as polyphenols. All of these are believed to be involved in reducing the risk of chronic diseases such as cardiovascular disease, diabetes and cancer.

Sources:
1) German Nutrition Society (http://www.dge.de)
2) Krauss RM, Eckel RH, Howard B, et al. AHA Dietary Guidelines. Revision 2000: A statement for healthcare professionals from the Nutrition Committee of the American Heart Association. J Nutr 2001;131:132-46.
3) US Food and Drug Administration. Qualified health claims: letter of enforcement discretion-nuts and coronary heart disease. Rockville MD: US Food and Drug Administration, 2003:1-4.
4) Rajaram S and Sabaté J. Nuts, body weight and insulin resistance. Br J Nutr 2006; 96:S79-S86.
5) Cassady BA, Hollis JH, Fulford AD, Considine RV and Mattes RD. Mastication of almonds: effects on lipid bioaccessibility, appetite, and hormone response. Am J Clin Nutr; 2009; Jan 14. [Epub ahead of print]

2. The positive effect of the Mediterranean diet enriched with nuts on metabolic syndrome

A recent study shows that the traditional Mediterranean diet enriched with nuts reduces the risk of the development of metabolic syndrome. Globally there is an increasing prevalence of the metabolic syndrome, affecting almost 25% of the adult population. Epidemiological studies suggest that unhealthy diets (i.e. Western-style diets) promote the occurrence of the metabolic syndrome, whereas Mediterranean diets, characterized by a high intake of fruits, vegetables, grains, fish and low-fat dairy products, have a protective role. Salas-Salvado et al. investigated the effect of a traditionally Mediterranean high fat diet on the occurrence of the metabolic syndrome.

1,224 participants aged between 55 and 80 years at a high risk of cardiovascular disease were assessed. The subjects were randomly assigned to one of three groups: one group received advice on a low-fat diet while the other two received advice on the Mediterranean diet. One Mediterranean diet group was provided with one litre of virgin olive oil per week and the other received 30 grams of mixed nuts per day.

After one year, the researchers evaluated the metabolic risk factors in the different diets. The traditional Mediterranean diet enriched with nuts reduced the prevalence of metabolic syndrome by 13.7 per cent, the diet with olive oil by 6.7 per cent, while the risk was only reduced by 2 per cent in the control group, according to findings published in the Archives of Internal Medicine.

While no changes in the body weight of the participants was recorded, the number of individuals with large waist circumference, high triglycerides or high blood pressure was found to have significantly decreased in the group that consumed the nuts, compared to the control group. The reversion of the abdominal obesity in the nut-eating Mediterranean group is thought to be an effect of the increased satiety, increased thermogenesis, fat malabsorption, and lower adiposity.

To conclude, this study showed that a non–energy-restricted traditional Mediterranean diet enriched with nuts, which is high in fat, high in unsaturated fat and palatable, is a useful tool in managing the metabolic syndrome.

Source:
1) Salas-Salvado J, Fernandez-Ballart J, Ros E, Martínez-González M-A, et al. Effect of a Mediterranean Diet Supplemented With Nuts on Metabolic Syndrome Status. Archive of Internal Medicine 2008; 22:2449-2458.

3. Nut consumption and the risk of long-term heart failure

Despite expectations, no relation could be found between long-term nut consumption and a reduced risk of heart failure in American males. The researchers expected to find a positive relation since nut consumption is associated with improved blood pressure, lower risk of diabetes, weight loss and lower risk of sudden death or death from coronary disease.

In the prospective cohort study, 20,976 male physicians were asked to report how often, on average, they had consumed nuts during the past year. A validated questionnaire was e-mailed to each participant every 6 months during the first year and was mailed annually thereafter to obtain information on nut consumption and the occurrence of new outcomes including heart failure. Participants were followed during an average of 19.6 years. During the study 1,093 new cases of heart failure were documented.

The results of the study show that participants who reported a nut consumption of more than two servings a week had a higher prevalence of the consumption of liquids, physical activity, breakfast cereal consumption and a lower proportion of smoking and hypertension. No relation was observed between nut consumption and incident heart failure. This lack of relation was seen in both lean and overweight participants.

The inability to differentiate between different types of heart failure and the lack of detailed information about the type of nuts that were consumed (e.g. roasted and salted, dry roasted, etc.) did limit the study. Furthermore, it is thought possible that physicians have different lifestyle habits from those of the general population. As well as over- or underreporting of nut consumption, the lack of data on other food intake could play a role in the unexpected outcome. Therefore the current study cannot rule out the possible beneficial effects of nut consumption on certain subtypes of heart failure, such as heart failure resulting from diabetic causes.

Source:
1) Djoussé L, Rudich T and Gaziono M. Nut consumption and risk of heart failure in the physicians health study. Am J Clin Nutr 2008; 88:930-933.