Metabolic responses to isoenergetic meals containing different proportions of carbohydrate and fat

Abstract

The purpose of the present study was to investigate the interrelationship between carbohydrate and fat metabolism at rest after isoenergetic meals of varying proportions of carbohydrate and fat. Eight physically-active subjects (BMI 18.1-23-4 kg/m2) were studied at rest on three occasions after an overnight fast. In a balanced design they were given meals containing carbohydrate, protein and fat in the following amounts respectively (g/70 kg body weight): meal 1 121,16,48; meal 2 70,16,70; meal 3 50, 14, 80. All meals were isoenergetic, containing 4-0 MJ/70 kg body weight, and were of similar appearance. In addition, on a fourth occasion five of the eight subjects consumed meal 4 (g/70 kg body weight): Carbohydrate 0, protein 0, fat 108. Blood samples were taken before eating the meal and at intervals following the meal to determine metabolic and hormonal responses. Energy expenditure and substrate oxidation were measured by indirect calorimetry and balance was calculated over the 5 h postprandial period. The incremental areas under the time curves for fat oxidation were greatest after meals 3 and 4 (P<O.O5), whereas incremental areas under the carbohydrate oxidation v. time curves were relatively reduced after these two meals (P < 0.05). This was accompanied by lesser suppression of plasma non-esterified fatty acid concentrations (P < 0.001) and reduced plasma insulin concentrations (P < 0.001) following these meals. Energy balance was almost identical after the three isoenergetic meals. In contrast, there was an inverse relationship between Carbohydrate and fat balance following these meals, with carbohydrate balance decreasing as carbohydrate intake decreased and fat balance increasing as fat intake increased. We conclude that there is a close interrelationship between carbohydrate and fat metabolism following isoenergetic meals in resting subjects. Isoenergetic meals: Substrate balance: Substrate oxidationIt is well established that carbohydrate and fat metabolism are interrelated (Randle et al. 1963), although the mechanisms regulating their relative oxidation rates are poorly understood. In human subjects the ability to adjust fat oxidation to fat intake appears to be less effective than the ability to adjust carbohydrate and protein oxidation to carbohydrate and protein intake respectively (Abbott et al. 1988). Flatt et al. (1985) reported that addition of 50 g fat to a mainly-carbohydrate breakfast caused no alteration in the oxidation of individual macronutrients over the subsequent 9 h, implying that all the additional fat had been stored. Similar findings have been reported from other studies over periods of up to 24h (Schutz et al. 1989;Bennett et al. 1992). In the study of Griffiths et al. (1994), addition of 80 g fat to a meal containing 80 g carbohydrate led to the subsequent oxidation of only 10 g additional fat, and the storage of 70 g. These studies compared carbohydrate

Impaired Fat Oxidation and Reduced Resting Energy Expenditure after a Fat Load in Individuals with Liver Steatosis

“…Previous studies, performed in healthy individuals, have shown opposite results for an acute fat load with regard to its effect on REE and fat oxidation [11,17,28]. In line with other investigations [6,29], no significant difference in the basal fat oxidation was demonstrated between individuals with vs. without hepatic fat accumulation.…”

“…The fat load consisted of 190 grams of a commercially available fresh cream (343 kcal/100 g; calories from fats, carbohydrates and proteins were 84% [17], 13% and 3% respectively; 70% saturated fatty acid, 0% cholesterol). The amount of the fresh cream (a dose equivalent to three full glasses) was chosen on the base of results of a previous investigation [3], taking into account the compliance of the participants to consume this food, assessed before the start of the study (190 g providing 652 kcal and containing 61 g of fats).…”

Carbohydrate and fat balance: separate existences or an intimate relationship?

“…By coincidence, our own study with an extremely similar design has also just been published (Whitley et al, 1997) and reaches almost identical conclusions. These studies show that there are intimate relationships between carbohydrate and fat oxidation after isoenergetic meals, such that the sum of their contribution to energy expenditure remains virtually identical, but the ratio varies according to the composition of the meal administered.…”

Metabolic, endocrine and mood responses to nocturnal eating in men are affected by sources of dietary energy

“…Since shift workers have increased risk of becoming obese [112], the impact of their food preference certainly requires investigation. During short-term (one to seven days) food intervention studies, healthy subjects have been able to adjust their macronutrient oxidation to the composition of isocaloric diets in most studies [3,15,68,91,97,99,129], whereas other studies have not found that fat oxidation correlates with fat intake [92,103]. The main reason for the divergent opinions regarding the high-fat diets role in the development of obesity is failure to take energy density into consideration.…”