Cardiovascular disease is the leading cause of death in Canada with annual direct and indirect costs estimated at $22 billion. Fasting lipid levels are associated with elevated risk of cardiovascular disease; however, postprandial lipids - the level of TG after a meal, are very potent predictors of cardiovascular disease risk because most of an individual's day is spent in the postprandial state. This problem is especially evident in obese individuals, who have an elevated postprandial TG response. An acute session of exercise is beneficial for reducing postprandial TG; however, caloric consumption immediately after exercise can attenuate this beneficial effect.
Carbohydrate quality may influence postprandial lipid response. Carbohydrates can be classified by their glycemic index (GI), where high GI carbohydrates are rapidly digested and result in large elevations in blood glucose. Low GI carbohydrates are digested slowly and result in a smaller, more gradual rise in blood glucose. High GI carbohydrates are associated with an elevated risk of cardiovascular disease and increased weight gain; whereas low GI carbohydrates are associated with a reduced risk of cardiovascular disease and decreased weight gain. As mentioned above, one of the main benefits of an acute session of exercise is to reduce TG levels after a subsequent meal. For example, an evening exercise session reduces the blood TG response after a high-fat breakfast provided the next day. This effect is negated if high GI beverages (i.e. sugar-sweetened drinks) are consumed immediately after exercise. Sports drinks such as Gatorade, and skim milk or chocolate milk are the leading beverages promoted for consumption during recovery after exercise. Gatorade has a high GI (i.e. GI=89) due to the inclusion of high amounts of simple sugars, whereas milk has a low GI (i.e. GI=34). Milk may therefore be a healthier choice for consumption after exercise.
No study has determined the effects of consuming low GI milk after an exercise session on next-day postprandial TG. Considering that consuming beverages after exercise is common practice and can influence blood lipid profiles, investigation into effects of low GI milk versus high GI recovery beverages is required.
The aim of this proposal is to determine if replacing calories expended during an evening session of endurance exercise with low GI milk can improve postprandial TG after a meal the next morning. We propose to look at the effects of consuming skim milk compared to Gatorade after endurance exercise on the blood TG, other lipids, glucose levels, and blood pressure responses after a high-fat meal consumed the morning after the exercise.
Our objective is to determine the effect of consuming milk after an evening exercise session on blood triglyceride response to a high fat meal the next morning. This will be compared to: A condition where exercise is performed followed by consumption of a high glycemic index Gatorade beverage; a condition where only exercise is performed with no after-exercise caloric consumption; a condition where neither exercise nor beverage is consumed in the evening. After each of these conditions, a high fat breakfast will be consumed the following morning (about 10 hours after the end of the exercise session). Blood will be collected before the breakfast and for 6 hours after the breakfast to determine postprandial metabolic response.
Our secondary objectives are to determine the effect of each condition on postprandial insulin, high density lipoprotein, apolipoprotein B, total cholesterol, and free fatty acids, and muscle fat oxidation. Blood pressure will also be assessed immediately after the evening exercise session and beverage consumption and continue throughout the night and throughout the postprandial period the next day.
Our primary hypothesis is that consuming low glycemic index milk after the evening exercise session will be superior to consuming Gatorade for reducing postprandial triglycerides the next morning.
Our secondary hypotheses are that consuming low glycemic index milk after the evening exercise session will be superior to consuming Gatorade for improving other metabolic measures (i.e. increasing high density lipoproteins, plasma free fatty acids, and fat oxidation, and reducing apolipoprotein B, low density lipoproteins, total cholesterol, and blood pressure) during the postprandial period after a high-fat meal.
