Importance of ketone bodies in endogenous fat transport

Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype?

Elite athletes and coaches are in a constant search for training methods and nutritional strategies to support training and recovery efforts that may ultimately maximize athletes’ performance. Recently, there has been a re-emerging interest in the role of ketone bodies in exercise metabolism, with considerable media speculation about ketone body supplements being routinely used by professional cyclists. Ketone bodies can serve as an important energy substrate under certain conditions, such as starvation, and can modulate carbohydrate and lipid metabolism. Dietary strategies to increase endogenous ketone body availability (i.e., a ketogenic diet) require a diet high in lipids and low in carbohydrates for ~4 days to induce nutritional ketosis. However, a high fat, low carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrate, which forms a key fuel source for skeletal muscle during intense endurance-type exercise. Recently, ketone body supplements (ketone salts and esters) have emerged and may be used to rapidly increase ketone body availability, without the need to first adapt to a ketogenic diet. However, the extent to which ketone bodies regulate skeletal muscle bioenergetics and substrate metabolism during prolonged endurance-type exercise of varying intensity and duration remains unknown. Therefore, at present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes’ performance under conditions where evidence-based nutritional strategies are applied appropriately.

Colonic fermentation from lactulose inhibits lipolysis in overweight subjects

One of the strategies to prevent insulin resistance is to reduce circulating free fatty acids (FFA). The aim of this study is to assess the effect of an oral lactulose load on fatty acid metabolism in overweight subjects. Eight overweight subjects received a primed constant intravenous infusion of [1-(13)C]acetate and of [1,1,2,3,3-(2)H(5)]glycerol for 9 h. After 3 h of tracer infusion, patients ingested 30 g lactulose, or saline solution. Arterialized blood samples were collected every 20 min. Basal plasma concentrations of acetate were similar before and between oral treatments as well as glycerol and FFA concentrations. Plasma acetate turnover was 11.4 +/- 2.4 vs. 10.7 +/- 1.4 micromol.kg(-1).min(-1) [not significant (NS)], and plasma glycerol turnover was 3.8 +/- 0.4 vs. 4.8 +/- 1.9 micromol.kg(-1).min(-1) (NS). After lactulose ingestion, acetate concentration increased twofold and then decreased to baseline. Acetate turnover rate increased to 15.5 +/- 2.2 micromol.kg(-1).min(-1) after lactulose treatment, whereas it was unchanged after saline treatment (10.3 +/- 2.2 micromol.kg(-1).min(-1), P < or = 0.0001). In contrast, FFA concentrations decreased significantly after lactulose ingestion and then increased slowly. Glycerol turnover decreased after lactulose ingestion compared with saline, 2.8 +/- 0.4 vs. 3.5 +/- 0.3 micromol.kg(-1).min(-1) (P < or = 0.05). A significant negative correlation was found between glycerol and acetate turnover after lactulose treatments (r = -0.78, P < or = 0.02). These results showed in overweight subjects a short-term decrease in FFA level and glycerol turnover after lactulose ingestion related to a decrease of lipolysis in close relationship with an increase of acetate production.

Uptake of beta-hydroxybutyrate in perfused hindquarter of starved and diabetic rats

To elucidate the peripheral ketone body uptake and the role of insulin in regulating peripheral ketone body utilization in starvation and diabetes mellitus, uptake of beta-hydroxybutyrate (BOHB) was investigated in the perfused hindquarter of starved (72 hour) or streptozotocin-induced (65 mg/kg, intraperitoneally) diabetic rats. Blood concentration of BOHB was significantly higher in diabetic (1,380 +/- 250 mumol/L) and starved (1,229 +/- 245 mumol/L) rats than in controls (104 +/- 8 mumol/L). The hindquarter was perfused with synthetic medium at a flow rate of 0.5 mL/g muscle weight/min. BOHB was added to the medium at a concentration of 0.1, 0.5, 2, or 10 mmol/L, and insulin was added at a concentration of 20, 100, or 500 microU/mL. In the hindquarter perfused with 0.1, 0.5, 2, or 10 mmol/L BOHB, fractional uptake of BOHB in the absence or presence of insulin was significantly lower in diabetic and starved rats than in controls. The addition of 100 or 500 microU/mL insulin significantly increased BOHB uptake in the perfused hindquarter of control rats; however, insulin addition did not significantly increase BOHB uptake in the perfused hindquarter of starved and diabetic rats. These results suggest that BOHB uptake is markedly reduced in the perfused hindquarter of starved and diabetic rats, and that physiological dose of insulin stimulates BOHB uptake in control rats, but not in starved and diabetic rats.

Ketone body production and disposal: effects of fasting, diabetes, and exercise

Turnover studies performed during progressive fasting in normal subjects indicate that the production rate and the concentration of KB rise markedly during the early phase of fasting and start reaching a plateau after about 5 days. In addition to increased production, a reduction in the metabolic clearance rate of KB contributes to the hyperketonemia. This reduced metabolic clearance rate reflects essentially the progressive saturation of muscular ketone uptake that occurs with increasing ketonemia. The hormonal and metabolic environment of fasting plays only a minor role in this process, since a fall in KB metabolic clearance similar to that observed during fasting is observed if hyperketonemia is artificially induced in the postabsorptive state by the infusion of exogenous ketones. As extraction of KB by muscle becomes limited during ongoing fasting, KB are preferentially taken up by the brain to serve as a substrate replacing glucose. The remarkable stability of ketonemia during prolonged fasting is maintained through the operation of a negative feedback mechanism whereby KB tend to restrain their own production rate. The antilipolytic and insulinotropic effects of KB are instrumental in this process. This homeostatic mechanism maintains ketogenesis only slightly above the maximal metabolic disposal rate, the difference corresponding to urinary excretion, which is always below 10% of total turnover under physiologic conditions. When type I insulin-deprived diabetic patients are compared at the same KB concentration with control subjects with fasting ketosis, the characteristics of KB kinetics are comparable in the two groups. The maximal KB removal capacity is identical in the two situations, and it is not possible to identify a ketone removal defect specific to diabetes. Thus, these data favor the concept that excessive production of KB represent the main factor leading to uncontrolled hyperketonemia. It should be realized that a production exceeding only slightly that prevailing during prolonged fasting is sufficient to cause a progressive build-up in concentration, leading to uncontrolled diabetic ketosis. In the overnight-fasted state, a prolonged exercise (2 h) performed at moderate intensity (50% VO2 max) stimulates the capacity of muscle to extract ketones from blood as evidenced by a stimulation of the metabolic clearance rate.(ABSTRACT TRUNCATED AT 400 WORDS)