Many animal studies have shown that diets high in MCT increase thermo-genesis, leading to less fat deposition as compared with diets high in LCT (Bray et al., 1980; Baba et al., 1982; Geliebter et al., 1983; Rothwell and Stock, 1987). An animal study by Lasekan et al. (1992), showed lower weight gain and 8-13% greater EE in rats fed a 3 : 1 mixture of MCT and LCT in emulsion compared with only LCT. Overall, animal studies suggest the possibility for MCT to increase EE in humans, thus potentially assisting in weight loss. The short-term effects of MCT on human EE are summarized in Table 14.1; long-term studies on EE are summarized in Table 14.2.
Human studies were first conducted by Flatt et al. (1985), who observed a greater postprandial (PP) thermogenesis and the tendency for a lower respiratory quotient, indicating a greater fat oxidation, over the first few hours following the consumption of a meal high in MCT compared with a meal high in LCT. This finding was reaffirmed by Seaton et al. (1986), in seven healthy men. Results demonstrated that mean PP oxygen consumption was 12% higher than basal values after the MCT meal, while it was 4% higher than the basal oxygen consumption after the LCT meal. However, these two studies examining the effect of MCT were one-meal effect and single-day experiments, which represent major limitations of these study designs.
A 1-week study assessed whether thermogenesis was affected differently in the presence of excess dietary energy as MCT in comparison to energy as LCT (Hill et al., 1989). Hill et al. (1989) recruited ten young males who were fed 150% of estimated energy requirements in a liquid formula diet containing 40% fat as either MCT or LCT. The authors demonstrated that excess dietary energy as MCT stimulated an increase in the thermic effect of food (TEF) to a greater degree than excess energy as LCT. This increase was seen on days 1 and 7 of the study and was most probably due to enhanced hepatic lipogenesis. The group recognized that the 1-week duration of the study was a limiting factor in determining the effects of MCT on basal metabolic rate (BMR) and body weight, as changes in these parameters could not be seen over such a short study period. Hence, it is was not known whether the effects of high-MCT diets on EE in humans found in short-term studies would persist in studies of longer duration and would produce weight loss even if energy intake remained constant.
Consequently, longer studies to assess the impact of MCT on EE were undertaken. White et al. (1999), fed 12 non-obese, premenopausal women a diet containing 40% of energy as fat, either in the form of butter and coconut oil or beef tallow, over 14 days. On day 7, mean BMR and PP EE values were significantly greater with the MCT diet than with the LCT diet. On day 14, PP total EE was still greater with the MCT diet, but not
Table 14.1 Human work on the acute effects (1 meal) of MCT on EE
Flatt et al., 1985
Randomized, cross-over study Controlled diet 7 young men
Seaton et al, 1986
Randomized, cross-over study Controlled diet 7 healthy men
Scalfi et al, 1991
Randomized, cross-over study Controlled diet 6 lean and 6 obese young men
Mixed 858kcal meal including 40 g MCT + lOg LCT or 50 g LCT
Test meal containing 48 g MCT or 45 g corn oil meal
Mixed meals including 38 g LCT or 30g MCT + 8g LCT
Dulloo et al, 1996
Randomized, cross-over study Combinations of MCT and LCT in the
Controlled diet following ratio of MCT:LCT (g/g):
Outcomes on EE
T Postprandial thermogenesis a'
■l Respiratory quotients, T fat oxidation 5-
T Postprandial oxygen consumption »
NS -i Respiratory quotients, T fat oxidation eg,
T 3-Hydroxybutyrate concentration
T Postprandial thermogenesis in the lean and the obese subjects
■I Respiratory quotients, T fat oxidation in the lean but not obese subjects
T EE with T MCT: LCT ratio
T 24-h EE with the diet providing a total of 15-30 g MCT «-»Respiratory quotients but trends towards -l
Van Wymelbeke et al., 2000
Randomized, cross-over study Controlled diet 12 healthy men
Binnert et al., 1998
Randomized, cross-over study Controlled diet 8 lean and 8 obese women
Bendixen et al., 2002
Randomized, cross-over study Controlled diet 11 healthy men
Kasai et al., 2002
Randomized, cross-over study Controlled diet 16 healthy men and women
4 lunches dietary carbohydrate, fat (« 43 g MCT or LCT), and a basic hypoenergetic lunch
Ingested 30 g (50 : 50) of MCT-LCT load or 30 g LCT (olive oil)
60% fat test meal, 4 different test fats: conventional fat (rapeseed oil); 3 modified fats (all 48% MCT) -lipase-structured fat, chemically structured fat, and physically mixed fat
Study 1: liquid meals including
10 g MCT or 5 g MCT + 5 g LCT or 10 g LCT Study 2: margarine or mayonnaise including 5 g MCT or 5 g LCT
^ EE after the different lunches i Carbohydrate oxidation was lower after the MCT and LCT lunches than after the Carbohydrate lunch i LCT oxidation in obese versus lean T MCT oxidation then LCT ^ MCT oxidation in obese versus lean
^ EE between fats
^ Substrate oxidation including fat oxidation ^ Appetite or ad libitum energy intake
T TEF after 5 g MCT + 5 g LCT and 10 g MCT i Respiratory quotients, T fat oxidation Study 2:
Abbreviations: MCT, medium-chain triglycerides; LCT, long-chain triglycerides; EE, energy expenditure; TEF, thermic effect of food; NS, non-significant.
Table 14.2 Human work on the chronic effect (>1 meal) of MCT on EE
Study diet including amount of MCT
Outcomes on energy expenditure
Hill et al., 1989
Randomized, cross-over study Controlled diet 10 non-obese men
White et al., 1999
Randomized, cross-over study Controlled diet 12 healthy women
St-Onge and Jones, 2003; St-Onge et al., 2003b
Randomized, cross-over study Controlled diet 24 overweight men
St-Onge et al., 2003a
Randomized, cross-over study Controlled diet 17 overweight women
Overfeeding period (150% of energy requirements) with 40% fat diet as ~185 g MCT or ~168 g LCT for 7 days
40% fat of total energy 2540 kcal (80% from experimental oil) as ~90 g MCT for 14 days
40% fat of total energy (75% from experimental oil) as functional oil composed of ~64.7 g MCT* (64.7% of fat) + PS (22 mg/kg body weight) + n-3 fatty acids (5 % of fat) versus ~100 g olive oil for 29 days
40% fat of total energy (75% from experimental oil) as functional oil composed of ~50 g MCT* (50% of fat) + PS (22 mg/kg body weight) + n-3 fatty acids (5 % of fat) versus ~100 g beef tallow for 27 days
T TEF on day 1 and day 5 T EE on day 7 i Fat oxidation in both diets T ß-hydroxybutyrate
^ BW, body fat T BMR on day 7 T Postprandial total EE on T Fat oxidation on days 1 and 7
T Postprandial EE and TEF on days 2 and 28 T EE on day 2, NST on day 28 T Fat oxidation on day 2, NST on day 28
i BW to same extent as beef tallow ^ RMR
^ Postprandial EE and TEF T EE on day 2 higher than day 27 T Fat oxidation on days 2 and 27
Abbreviations: BW, body weight; EE, energy expenditure; MCT, medium-chain triglycerides; LCT, long-chain triglycerides; NS, non-significant; PS, plant sterol; RMR, resting metabolic rate; TEF, thermic effect of food.
* Calculated based on 3000 kcal.
significantly. The authors concluded that short-term feeding of MCT-enriched diets increases total EE, but this effect may not be sustained with continued feeding. In addition, MCT were suggested to exert greater incremental increases in EE when given in a single dose than during chronic intake. In order to further explore the outcome of long-term MCT intake, a 27-day study was carried out to determine the effects of MCT versus LCT consumption in 17 obese healthy women (St-Onge et al., 2003a). Long-term consumption of MCT enhanced both EE and fat oxidation on day 2, as well as on day 27, when compared with LCT consumption. A similar protocol conducted in 19 overweight men for 28 days showed comparable results, with average EE and fat oxidation being greater on day 2 and showing a tendency to increase on day 28 with MCT as compared with LCT consumption (St-Onge and Jones, 2003; St-Onge et al., 2003c). These human studies demonstrated an evident increase in EE, especially in men. When data are extrapolated from trials conducted in men, the average EE is approximately 460 kJ/day greater with MCT than with LCT consumption. In contrast, data from women show differences in EE of 138 kJ/day between MCT and LCT. Using the peak difference in EE between MCT and LCT in men, it has been determined that a weight gain of 1.35 kg in 30 days could be avoided by substituting MCT for LCT. Using the lowest difference in EE between MCT and LCT, both men and women could avoid a weight gain of 0.45 kg per 30 days by consuming MCT rather than LCT.
The ingestion of MCT in low to moderate quantities may have variable effects on TEF. Dulloo et al. (1996), fed subjects 15-30 g of MCT in addition to a weight-maintaining diet containing 40% of energy as fat. It was reported that EE increased significantly with increasing MCT : LCT ratio. Furthermore, the difference in 24-h EE between 30 g of MCT and 30 g of LCT was 471 kJ; this increase in EE would result in about 0.45 kg of fat loss over 36 days if effects were to persist over that period. However, even smaller doses of MCT (5 and 10 g/day) have been tested (Kasai et al., 2002). Results have shown that intake of small doses of MCT causes larger diet-induced thermo-genesis than LCT. Therefore, both small and large doses of MCT increase EE; however, large doses may create greater TEF, which may be more beneficial for weight loss.
There may be differences in the effect of MCT on TEF between lean and obese individuals. Scalfi et al. (1991) first tested this possibility. Their results demonstrated that PP thermogenesis was enhanced in both lean and obese subjects when LCT were replaced with MCT, but that MCT-induced thermogenesis tended to be higher in obese than in lean individuals. Similarly to the previous study, Binnert et al. (1998), showed that LCT were less well oxidized in obese than in control subjects when consuming a mixed 50% LCT and 50% MCT load. The authors suggested that obesity may be associated with a defective oxidation of LCT, probably related to excessive intake of meal-derived LCT. Thus, substitution of MCT for LCT
in combination with a weight-maintaining diet might prevent long-term weight gain via increased EE.
There is clear evidence that MCT create an increase in TEF in both animal and human studies within the first week of intake; however, some metabolic adaptations to MCT may occur afterwards as demonstrated in long-term feeding studies. This metabolic regulation may be due to weight loss, and techniques should be sought to avoid this metabolic adaptation. Furthermore, the effects of MCT on PP thermogenesis seem to be dose dependent, although even small doses can increase PP thermogenesis. In addition, MCT are oxidized at a faster rate than LCT which may suggest that they will lead to less fat accumulation and subsequent weight loss.
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