naturalofcourse
Thu, July 1st, 2004, 11:19 AM
Another NASM article written by Apex Fitness Group (http://www.apexfitness.com/)
Several studies have shown that exercise’s contribution to successful weight loss is quite small compared to the contribution of a low-calorie diet. And while most people agree that exercise combined with a proper diet is the best way to induce and maintain weight loss, there is controversy about the benefits or detriments of eating a morning meal before a workout.
The typical argument for morning exercise on an empty stomach is that it will result in more fat burned. The theory is that after a night of sleep, glycogen stores (in the liver) and blood sugar are low. If one performs cardiorespiratory exercise before eating, the body will use a higher percentage of calories from fat, translating into more fat burned for the dieter.
The first part of this argument—that more fat is oxidized as a result of little carbohydrate availability—is easily supported by science. Research shows that when the body is in a fasted state, it burns more fat during cardiovascular exercise. But if food is consumed (in this case carbohydrates) before exercise, there is a greater reliance on burning carbohydrate rather than fat. Why? Because carbohydrates are preferentially oxidized or burned when present.
The insulin response from carbohydrate ingestion reduces lipolysis, fatty acid release and fat oxidation. In fact, what one has consumed in the 24 hours preceding an exercise session can affect fat oxidation. Looking at fat oxidation by itself during an exercise session to determine the efficacy of the session for fat loss misses the lion's share of the story. The respiratory quotient (RQ) is the ratio of the oxygen inhaled to the CO2 expelled by the body. RQ is influenced by macronutrient percentages in the diet and tells a scientist how much fat or carbohydrate oxidation changes when all else is held constant. In addition to diet, a negative energy balance offsets the RQ and decreases it in favor of fat oxidation.
Carbohydrate and protein oxidation are both directly related to acute changes in their intake. In other words, a diet high in carbohydrate increases carbohydrate oxidation (RQ) and decreases fat oxidation. A large increase in protein consumption creates the same compensatory decrease in fat oxidation. Whether these changes in macronutrient intake increase fat stores on the body depends on energy balance. According to some, the way to test this is to measure RQ in relation to the food quotient (FQ). FQ is the ratio of carbon dioxide produced to oxygen consumed during the oxidation of foods representative of the habitual diet. When the RQ to FQ ratio (RQ/FQ) is less than one, it means that calorie intake is less than 24-hour energy expenditure. When RQ/FQ is greater than one, the opposite is true.
So what should we eat before our morning cardio? Just because a study shows fasting participants had a higher fat oxidation during exercise than fed subjects does not mean that an equivalent amount of body fat won't be lost at the end of the day as long an equivalent amount of calories were expended.
Consider a study by Schneiter et al, which showed that the percentage of fat burned by those exercising in a fasted state is higher than in those who ate before exercising. Both groups consumed the same calories during the eight-hour study period. The only difference between the two trials was that one trial was done in a fasted state with all food consumed after exercise. The other trial was performed with the same number of calories consumed before exercise. The biggest result from this study was that total calories expended during exercise and the eight-hour study period was the same in both trials. The meal-before-exercise group burned slightly more carbohydrate during the eight hours and the exercise-before-meal group burned more fat. Keep in mind that the groups did 45 minutes of high-intensity exercise (~8 METs) yet the fasted group burned only 10g of fat more in the eight-hour study period than the group that ate before exercising. This adds up to about a third of an ounce of fat. At this rate, it would take 45 days of exercise to burn one pound of fat with the differences between the groups! Thankfully, this is not where the bulk of fat loss resides for a typical client.
In reality, while the percentage of fat used during exercise varies depending on carbohydrate available, the most important thing for a client seeking fat loss is how many calories are burned during their training. The more calories used during exercise, the greater the total energy expenditure will be for that day, and the more stored fat will be lost at the same calorie intake. For example, Amy has a fat-loss goal and maintenance calorie level of 2,000 per day. She eats 1,500 calories daily and exercises four times per week. If she follows a 20/60/20 diet, she will consume 60 percent or 900 calories of carbohydrate daily in addition to 600 calories of protein and fat. If she wakes on Monday and exercises on an empty stomach for 30 minutes at 65 percent VO2 max, she’ll burn fat and muscle glycogen as illustrated in the above studies.
Throughout the rest of the day she has 1,500 calories to consume. She’ll use about 500 calories of stored fat to make up for the energy deficit. If she eats 300 calories of carbohydrate on Tuesday before exercising with the same duration and intensity, she burns much of the exogenous carbohydrates and less fat during exercise than on Monday. She now has only 1,200 calories to eat for the rest of the day and is still in a 500- calorie deficit. The result is that she will burn more stored fat during the post-exercise period on Tuesday than on Monday in contrast to the extra stored fat lost during exercise on Monday. The loss of stored body fat for Monday will be identical to Tuesday because her energy intake and expenditure is identical on both days. If the eight-hour study by Schneiter were performed on individuals in an energy deficit over a 24-hour period, the 10-gram difference would probably have been erased as the energy deficit forced the use of stored fat throughout the day.
Athletes have long known that performing cardiovascular exercise for more than an hour at a high intensity may require carbohydrates to sustain the activity. A study by Schabort et al concluded that subjects who consumed a breakfast before exercising had an increased time to fatigue compared to the fasted subjects. Because most dieters seeking fat loss don’t exercise to exhaustion, much less exceed an hour of cardio training, this is a moot point. This discussion does not change the fact that performance/endurance athletes need to be adequately nourished before and during endurance activity.
The ultimate decision about whether to eat before a morning workout comes down to preference. Some people need to eat before they exercise or they get lightheaded, dizzy or fatigue quickly. Others just feel better with food in their stomach, which may lead to a higher-intensity workout and more calories burned not only during the routine but also afterward (excess post-exercise oxygen consumption, or EPOC). For those who consume food before exercising in the morning, they should be aware that certain types of food might have a negative effect on their performance and should avoid too much or certain foods that upset the stomach.
Several studies have shown that exercise’s contribution to successful weight loss is quite small compared to the contribution of a low-calorie diet. And while most people agree that exercise combined with a proper diet is the best way to induce and maintain weight loss, there is controversy about the benefits or detriments of eating a morning meal before a workout.
The typical argument for morning exercise on an empty stomach is that it will result in more fat burned. The theory is that after a night of sleep, glycogen stores (in the liver) and blood sugar are low. If one performs cardiorespiratory exercise before eating, the body will use a higher percentage of calories from fat, translating into more fat burned for the dieter.
The first part of this argument—that more fat is oxidized as a result of little carbohydrate availability—is easily supported by science. Research shows that when the body is in a fasted state, it burns more fat during cardiovascular exercise. But if food is consumed (in this case carbohydrates) before exercise, there is a greater reliance on burning carbohydrate rather than fat. Why? Because carbohydrates are preferentially oxidized or burned when present.
The insulin response from carbohydrate ingestion reduces lipolysis, fatty acid release and fat oxidation. In fact, what one has consumed in the 24 hours preceding an exercise session can affect fat oxidation. Looking at fat oxidation by itself during an exercise session to determine the efficacy of the session for fat loss misses the lion's share of the story. The respiratory quotient (RQ) is the ratio of the oxygen inhaled to the CO2 expelled by the body. RQ is influenced by macronutrient percentages in the diet and tells a scientist how much fat or carbohydrate oxidation changes when all else is held constant. In addition to diet, a negative energy balance offsets the RQ and decreases it in favor of fat oxidation.
Carbohydrate and protein oxidation are both directly related to acute changes in their intake. In other words, a diet high in carbohydrate increases carbohydrate oxidation (RQ) and decreases fat oxidation. A large increase in protein consumption creates the same compensatory decrease in fat oxidation. Whether these changes in macronutrient intake increase fat stores on the body depends on energy balance. According to some, the way to test this is to measure RQ in relation to the food quotient (FQ). FQ is the ratio of carbon dioxide produced to oxygen consumed during the oxidation of foods representative of the habitual diet. When the RQ to FQ ratio (RQ/FQ) is less than one, it means that calorie intake is less than 24-hour energy expenditure. When RQ/FQ is greater than one, the opposite is true.
So what should we eat before our morning cardio? Just because a study shows fasting participants had a higher fat oxidation during exercise than fed subjects does not mean that an equivalent amount of body fat won't be lost at the end of the day as long an equivalent amount of calories were expended.
Consider a study by Schneiter et al, which showed that the percentage of fat burned by those exercising in a fasted state is higher than in those who ate before exercising. Both groups consumed the same calories during the eight-hour study period. The only difference between the two trials was that one trial was done in a fasted state with all food consumed after exercise. The other trial was performed with the same number of calories consumed before exercise. The biggest result from this study was that total calories expended during exercise and the eight-hour study period was the same in both trials. The meal-before-exercise group burned slightly more carbohydrate during the eight hours and the exercise-before-meal group burned more fat. Keep in mind that the groups did 45 minutes of high-intensity exercise (~8 METs) yet the fasted group burned only 10g of fat more in the eight-hour study period than the group that ate before exercising. This adds up to about a third of an ounce of fat. At this rate, it would take 45 days of exercise to burn one pound of fat with the differences between the groups! Thankfully, this is not where the bulk of fat loss resides for a typical client.
In reality, while the percentage of fat used during exercise varies depending on carbohydrate available, the most important thing for a client seeking fat loss is how many calories are burned during their training. The more calories used during exercise, the greater the total energy expenditure will be for that day, and the more stored fat will be lost at the same calorie intake. For example, Amy has a fat-loss goal and maintenance calorie level of 2,000 per day. She eats 1,500 calories daily and exercises four times per week. If she follows a 20/60/20 diet, she will consume 60 percent or 900 calories of carbohydrate daily in addition to 600 calories of protein and fat. If she wakes on Monday and exercises on an empty stomach for 30 minutes at 65 percent VO2 max, she’ll burn fat and muscle glycogen as illustrated in the above studies.
Throughout the rest of the day she has 1,500 calories to consume. She’ll use about 500 calories of stored fat to make up for the energy deficit. If she eats 300 calories of carbohydrate on Tuesday before exercising with the same duration and intensity, she burns much of the exogenous carbohydrates and less fat during exercise than on Monday. She now has only 1,200 calories to eat for the rest of the day and is still in a 500- calorie deficit. The result is that she will burn more stored fat during the post-exercise period on Tuesday than on Monday in contrast to the extra stored fat lost during exercise on Monday. The loss of stored body fat for Monday will be identical to Tuesday because her energy intake and expenditure is identical on both days. If the eight-hour study by Schneiter were performed on individuals in an energy deficit over a 24-hour period, the 10-gram difference would probably have been erased as the energy deficit forced the use of stored fat throughout the day.
Athletes have long known that performing cardiovascular exercise for more than an hour at a high intensity may require carbohydrates to sustain the activity. A study by Schabort et al concluded that subjects who consumed a breakfast before exercising had an increased time to fatigue compared to the fasted subjects. Because most dieters seeking fat loss don’t exercise to exhaustion, much less exceed an hour of cardio training, this is a moot point. This discussion does not change the fact that performance/endurance athletes need to be adequately nourished before and during endurance activity.
The ultimate decision about whether to eat before a morning workout comes down to preference. Some people need to eat before they exercise or they get lightheaded, dizzy or fatigue quickly. Others just feel better with food in their stomach, which may lead to a higher-intensity workout and more calories burned not only during the routine but also afterward (excess post-exercise oxygen consumption, or EPOC). For those who consume food before exercising in the morning, they should be aware that certain types of food might have a negative effect on their performance and should avoid too much or certain foods that upset the stomach.