This study is one of the few studies to examine the effect of MCT consumption on body composition in an ad libitum setting. It is also the longest study to examine the effects of MCT consumption on body composition to date. We have shown that the inclusion of MCT oil in a weight-loss program leads to greater weight loss than does the inclusion of a similar amount of olive oil. However, we were not able to show differences in adipose tissue distribution between the different diets.
In this study, we found that subjects consuming MCT as part of their weight-loss diet lost an average of 1.7 kg more than did subjects consuming olive oil as part of their weight-loss diet. This agrees with our previous data (12
) and hypothesis put forth previously concerning the potential for enhanced weight management with MCT consumption (19
). In our previous study, we found that women burn ≈45 kcal/d more when consuming medium-chain saturated fats than when consuming long-chain saturated fats (12
). In addition, studies have found that subjects consume an average of 62.5 kcal/d less when meals contain MCT instead of LCT (19
). The addition of an enhanced thermic effect of food and reduced food intake would result in a lower caloric retention of 107.5 kcal/d. This lower caloric retention, if maintained over a 16-wk period, would lead to an additional loss of 1.55 kg body wt with MCT consumption than with LCT. Our finding of a 1.7-kg difference in weight loss thus agrees with our earlier hypothesis (19
Our results also agree with those of previous clinical studies (14
). Tsuji et al (15
) found that overweight subjects consuming a diet containing ≈10 g MCT oil/d for 12 wk lost 1.34 kg more than did a group consuming 10 g of an LCT oil (rapeseed oil–soybean oil blend). If their data extrapolate to 16 wk, their subjects could have lost 1.79 kg more with MCT oil consumption than with LCT oil. Similar results were also obtained with subjects consuming 5 g of MCT or LCT oil/d (14
). In that study, weight loss over a 12-wk period was enhanced by 1.3 kg, which could extrapolate to 1.7 kg over a 16-wk period. Weight-loss data from these 2 studies, extrapolated to 16 wk, are similar to those obtained in the present study.
In a previous controlled feeding study, we found that men had greater reductions in upper-body adipose tissue after consuming MCT oil for 4 wk than after consuming olive oil for 4 wk (13
). In this study, we did not find a significant diet-by-week interaction for any of the adipose tissue subcompartment measurements. Our sample size may have been too small to detect these changes. Our study was originally powered to detect a 1.2-kg difference between groups in change in absolute fat mass. We had estimated requiring 18 subjects/group to detect this difference with 95% confidence and 80% power. We found a difference of 1.5 kg in change in total fat mass between groups with 15 and 16 subjects in each group. A larger sample size may be necessary to detect significant changes in adipose tissue subcompartments. Alternatively, it may be that there are sex differences in adipose tissue mobilization response to MCT. In a previous study of women, we had not found any significant differences in adipose tissue compartment losses between MCT and LCT consumption as part of a weight maintenance diet for 4 wk (12
), and we had also proposed a potential sex effect on the basis of a review of the literature (19
). In this study, the larger number of women relative to men may have also influenced our results.
A further limitation of the present study is the large dropout rate (36.7%), which was comparable between groups. However, this number is similar to what occurred in a previous 12-wk weight-loss study by our group (20
) and similar to that observed by other groups as well (21
). Moreover, dropouts did not introduce any systematic bias into our sample because there were no differences in body composition or other baseline characteristics among the completers of each group at baseline.
We chose olive oil as a control oil for several reasons: 1
) it has physical properties similar to those of MCT oil (liquid at room temperature and can be satisfactorily used for cooking, baking, and as a salad dressing), 2
) we previously found differences in diet-induced thermogenesis between olive oil and MCT oil consumption, and 3
) it is considered to be a healthy oil and is widely used. However, some studies have found that olive oil consumption can lead to favorable changes in body composition (23
) and increased fat oxidation (25
) relative to animal-derived saturated fats. Piers et al (25
) found that postprandial fat oxidation after a meal rich in olive oil was greater than after a similar meal high in saturated fat from cream. In a follow-up study with a small group of overweight men, Piers et al (24
) found that consuming a diet rich in monounsaturated fats, mostly from olive oil, led to lower body weight, fat mass, percentage body fat, and trunk fat mass than did consuming a diet rich in saturated fat from animal products for 28 d. They suggested that replacing saturated fat in the diet with monounsaturated fat can result in small but significant reductions in body weight and fat mass. A similar study was recently done examining the effects of 3 diets rich in saturated fat, monounsaturated fat, or carbohydrates on body composition and fat distribution (23
). There was no difference in energy intake or resting energy expenditure between diets, but fat oxidation was higher after the subjects consumed the diets rich in monounsaturated fat and saturated fats than after the diet rich in carbohydrates. When they examined body composition, they found higher trunk fat mass and lower leg fat mass after subjects consumed the high-carbohydrate diet than after the high-saturated-fat and high-monounsaturated-fat diets. There was no significant change in total body weight or lean body mass. These authors also suggested that the macronutrient composition of the diets may influence body fat distribution without necessarily affecting total body weight.
From these studies, we may hypothesize that our results are conservative. If olive oil produces favorable body composition relative to an animal-product-derived saturated fat and relative to a high-carbohydrate diet, it is possible that greater differences between groups would have been observed in this study if we had chosen a long-chain saturated fat control or a high-carbohydrate control group. We showed previously that MCT oil enhances diet-induced thermogenesis compared with long-chain saturated fats from beef tallow (12
). However, although differences in energy expenditure corresponded to differences in body weight, we did not find significant differences in body composition between diets. Furthermore, the animal-derived saturated fat control was not considered desirable by some subjects and was not well tolerated. It is also impossible to blind subjects to treatment oil when oils have such different properties: MCT oil is liquid at room temperature, whereas animal-derived long-chain triacylglycerol fats are solid. A future study comparing the effects of a weight-loss diet high in MCT oil with one high in carbohydrates may show greater benefits of MCT oil consumption for weight loss.
In conclusion, the results of this study show that a weight-loss diet that incorporates moderate amounts of MCT oil leads to greater losses of body weight and fat mass than does consumption of an equivalent amount of olive oil. Although this study cannot distinguish which side of the energy balance equation played a bigger role in this differential weight loss (enhanced suppression of food intake or enhanced thermic effect of food), these data complement the body of literature concluding that MCT oil can be successfully used in a weight-management program to enhance weight loss. This study also shows that fats have a place in a weight-loss diet and that choosing MCT oil over an LCT oil may provide an additional boost for weight loss.