|Posted on December 11, 2020 at 1:25 PM|
Effects of Different Dietary Fatty Acids on Human Energy Balance, Body Weight, Fat Mass, and Abdominal Fat
Sze Yen Tan, in Nutrition in the Prevention and Treatment of Abdominal Obesity, 2014
The effects of increased MUFA intake on body weight and body composition were investigated using a within-subject crossover and a randomized controlled experimental design (Table 36.1). In one crossover study, 16 adults with type 2 diabetes mellitus (T2DM) received two test diets, one high in carbohydrate and another high in MUFA (from olive oil), for 3 months per diet (separated by a 1-month washout period). Total body fat mass decreased after the intervention periods but was not significantly different between the two diets. However, there appeared to be a trend of different fat mass loss patterns: participants lost upper body fat with the MUFA diet but gained upper body fat slightly during the high-carbohydrate diet. When examined as a ratio of upper-to-lower body fat mass, the high-carbohydrate diet induced a significantly higher ratio than the high-MUFA diet (P < 0.01) . A more recent crossover study that fed 11 insulin-resistant adults high-SFA, high-MUFA, and high-carbohydrate diets in a random order for 28 days each also failed to document additional effects of increased MUFA intake on body weight and fat mass loss. However, the MUFA-rich diet did prevent upper body fat accumulation that was induced by the high-carbohydrate diet. Consequently, the upper-to-lower body fat ratio was significantly higher in that diet group . Similar to the aforementioned studies, one study documented greater upper body fat loss after following a high-MUFA diet (vs. a high-SFA diet) for 4 weeks . This study also recorded significant losses in body weight and total body fat mass, which was not found in the other two studies. Differences in the study populations may explain the contradictory observations regarding total body fat mass loss: studies that included adults with T2DM or insulin resistance reported no additional benefits of MUFA on body weight and fat mass, while studies that recruited healthy male adults did. Impaired fatty acid oxidation has been previously reported in adults with T2DM [104,105].
The randomized controlled, parallel-arm studies that tested the effects of MUFA on body weight and body composition are limited, and were conducted using a weight loss paradigm. In one study, 57 overweight and obese adults were randomly assigned to follow a low-fat, high-protein (30% fat, 35% protein) or a high-fat, standard-protein (45% fat high in MUFA from mixed nuts and canola oil and 18% protein) diet . During the first 12 weeks of this trial, energy restriction was prescribed to promote weight loss; this was followed by an energy balance period of 4 weeks. This study did not find significant differences in body weight and fat mass loss between the two diets. The lack of effects of MUFA in this trial may be due to (1) the simultaneous manipulation of two dietary components (e.g. protein and fat); (2) the absence of a proper control group; (3) subtle acute physiological effects of MUFA that failed to translate into clinical observations; or (4) adaptation of the body to increased dietary MUFA during the study period. However, these possibilities are yet to be evaluated.
Another randomized controlled trial compared the weight- and fat-mass-reducing effects of a high-MUFA (from almonds) vs. a high-carbohydrate energy-restricted diet for 24 weeks . Like the previous study, the two intervention diets differed in more than one aspect: the MUFA diet contained higher total fat and lower carbohydrate (39% fat, 32% carbohydrate) than the high-carbohydrate diet (19% fat, 53% carbohydrate). In this study, greater reductions in weight (−18% vs. −11%), fat mass (−30% vs. 20%), and waist circumference (an indicator of abdominal fat; −14% vs. −9%) were observed in the high-MUFA group, although it should be pointed out that these superior clinical outcomes may not be attributable to MUFA alone. Almonds (the vehicle of MUFA used in this study) influence energy balance by promoting satiety [108,109] and dietary compensation [110–112], and the absorption of dietary fat from almonds is lower than previously thought . In summary, the presence of confounding factors in the intervention studies limits the ability to draw conclusions as to whether MUFA has therapeutic effects on body weight and total fat mass reduction. More longer-term and better-controlled intervention trials are therefore warranted.
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