Original articleAcute effects of three high-fat meals with different fat saturations on energy expenditure, substrate oxidation and satiety
Introduction
Nuts and olive oil are important components of the Mediterranean diet that are believed to have salutary health effects. Several large epidemiological studies have associated the frequency of nut consumption with reduced risks of coronary heart disease, sudden death, and all-cause mortality and diabetes.1 High consumption of olive oil has also been associated with protection from myocardial infarction2 and total mortality.3 Cardiovascular protection by nuts and olive oil may be explained by their biochemical composition. Although rich in fat, these foods have a low content of saturated fatty acids (SFA) but a high content of unsaturated fatty acids, mainly polyunsaturated fatty acids (PUFA) in walnuts and monounsaturated fatty acids (MUFA) in olive oil. Nuts and olive oil are also rich in vitamins, antioxidants and diverse phytochemicals.4, 5
The evidences accumulated on the salutary effects of regular nut and/or olive oil intake have prompted inclusion of these foods in the dietary guidelines of the American Heart Association/National Heart, Lung, and Blood Institute and other scientific societies. Also, the U.S. Food and Drug Administration has endorsed the consumption of these typical Mediterranean foods for cardiovascular disease prevention. However, nuts and olive oil are fatty foods, and the common perception that they provide excess energy and thus promote obesity has had a negative effect on their image. Several lines of evidence suggest that this concern can be dispelled. Thus, in a cross-sectional analysis of the Nurses Health Study, regular nut consumption was associated with lower, not higher body mass index (BMI).6 Recently, high intakes of olive oil or nuts were not associated with weight gain or the risk of overweight or obesity in a prospective study of a large Mediterranean cohort.7, 8 Moreover, prospective studies have suggested an inverse relationship between frequent nut consumption and BMI.6 Finally, several feeding trials have shown that nut or olive oil consumption, even in large amounts, either was not associated with increases in body weight or BMI9 or the increase observed was much less than predicted.10
The neutral or even salutary effects of nuts and olive oil on adiposity may be explained by several mechanisms. In the case of nuts, studies have shown that intake has a satiating effect, whereby consumption of other energy-dense foods is curtailed11; intestinal absorption of fat components is limited12; or intake may be associated with increased thermogenesis and a decrease in the ability of fat to be oxidised.4, 9 It has also been suggested that olive oil consumption is associated with increases in satiety, thermogenesis, and fat oxidation.13, 14 Nevertheless, few studies designed specifically to evaluate the effect of nut or olive oil consumption on energy balance and body weight have been performed.15, 16
Although there are controversies,17, 18 experimental evidences suggest a greater satiating and thermogenic effect of unsaturated fatty acids than SFA.19 However, the acute effects of nut or olive oil consumption on thermogenesis, substrate oxidation and satiety have not been sufficiently studied.14, 15
The aim of this study was to assess the effects of the acute consumption of three isocaloric high-fat meals differing in fat quality on resting metabolic rate (RMR) and postprandial thermogenesis, substrate oxidation and satiety in healthy men.
Section snippets
Subjects
Healthy male volunteers aged between 18 and 30 years were invited to participate in an unblinded randomised crossover trial aiming to compare the acute metabolic effects of three test meals. A Latin square design with three test meals and three feeding periods was used. Participants were individually randomised in a crossover design among three meal sequences (high-fat meals with walnuts, olive oil or dairy fat) and were studied on three separate days 1–2 weeks apart. The volunteers were
Results
Of the 36 adult subjects initially screened, six were not included because they had a BMI lower than required (n = 2) or difficulty in attending the tests (n = 4). One volunteer dropped out for personal reasons after randomisation. The characteristics of the 29 participants randomised into the study and completing all three test meals are presented in Table 1. Participants were healthy men, aged between 18 and 30 years, and had a variable degree of adiposity.
The nutritional composition of the test
Discussion
It is well established that high-fat diets predispose to obesity. This was supported by the evidence that fat balance is maintained far less accurately than carbohydrate and protein balance.26 In fact, fat oxidation rates appear to be determined mainly by the difference between energy expenditure and carbohydrate and protein oxidation.
Recent evidences suggest that the overall amount of fat intake is not the only factor determining fat stores. Fat quality is important as well. In fact, the
Conflict of interest
JSS has received research funding from the International Nut Council, Reus, Spain. He is a nonpaid member of the Scientific Advisory Board of the International Nut Council. ER has received research funding from the California Walnut Commission, Sacramento, CA and is a nonpaid member of its Scientific Advisory Committee.
The authors have no other conflict of interest to declare.
Acknowledgements
This study was supported by the Spanish Ministry of Education and Science (CICYT-AGL2005-0365), Spanish Ministry of Health (RTIC RD06/0045), and the International Nut Council. Ciber Fisiopatología de la Obesidad y Nutrición (CIBEROBN) is an initiative of ISCIII. Borges S.A. from Reus donated the walnuts used in the study. Patricia López-Uriarte is a recipient of a predoctoral fellowship from the Generalitat de Catalunya's Ministry of Universities, Research and the Information Society. We thank
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