Atkins Diet Physiology: Metabolic or Not?

In this study, we examined the effects of a high fat/low-carbohydrate diet on body weight and composition, in comparison to the effects of a calorie-reduced, fat-restricted diet. We conducted this particular study in an effort to answer the question of whether weight loss occurs because of a metabolic advantage, where the body begins to use fat as energy due to a lowered carbohydrate intake, or because of a negative energy balance, where the energy expenditure of an individual is higher than the energy intake. Our findings suggest that weight loss occurs because of a negative energy balance, which supports other studies on calorie theory (Golay, et al., 1996; Freedman, et al., 2001).

By comparing the total daily calorie intake of subjects on the conventional diet to those on the Atkins diet, it was found that subjects on the Atkins diet achieved a greater reduction in calorie intake over the six-month study than subjects on the conventional diet (724 kcal/month Vs 496 kcal/month). In addition, body weight and overall body fat were also lower over the six-month period for those on the Atkins diet (16.2 kg & 8.1 Vs 10.8 kg & 5.2).

One possible explanation for these findings is that subjects on the Atkins diet may have experienced greater satiety, or satisfaction in relation to hunger, due to higher levels of fat content in the food sources designed for lower carbohydrate intake. A study by Cecil (et al., 1999) supports the concept that high-fat diets are more satiating than high carbohydrate meals. In the Cecil study, nine individuals were given high fat foods on one occasion and high carbohydrate foods on another occasion. Levels of satiety ratings were taken 2 hours after the meal, and the results showed that ingestion of high fat foods suppressed hunger and induced fullness more than the ingestion of high carbohydrate food.

It should be noted that in a 1999 study, Holt and his colleagues’ results contradicted those in this study and those in the Cecil study by claiming that a high-carbohydrate diet increased satiety. In the Holt study, fourteen participants were given four breakfasts on four random mornings, two of which consisted of high fat content, and two of which consisted of high carbohydrate content. Following the meal, participants left the research center, and recorded appetite and alertness ratings throughout the day. Holt interpreted the results to find that the high carbohydrate meals were more satiating than the high fat meals, and resulted in less food consumption during later meals for the subjects.

However, there was a flaw in the methods of Holt (et al., 1999). After the subjects ate their provided breakfasts at the research center, they were able to leave to continue normal day activities, including normal eating behaviors. Even Holt admits that subjects who consumed the high fat, low carbohydrate meal at the center may have simply gone back to normal eating habits of higher carbohydrates during the rest of day, which “may be a compensatory response to ingest a sufficient amount of food…to match the level of fullness produced by the subjects’ habitual breakfasts” (Holt, et al., 1999). In other words, the subjects may not have been reacting to levels of satiety, but rather, to habitual levels of food intake.

Our study did not restrict a calorie intake for the subjects on the Atkins diet, and yet the results showed these subjects actually achieved a greater reduction in calorie intake over the sixth month period, as well as a greater reduction in body fat and weight. This leads to the proposition that subjects on the Atkins diet chose to eat less food in their own, indicating that their high-fat, low carbohydrate diet increased feelings of satiety. This reduction in food in turn reduced their overall calorie intake, creating a negative energy balance. Since the subjects were isolated in a resort and were under strict observation, we can conclude that these individuals followed their diets accordingly, thereby eliminating the possibility that these individuals ate foods other that the high fat, low carbohydrate foods intended in the study. Additionally, we can discount the notion that the subjects may have been exercising, thus negating any possibility that higher levels of exercise were the cause of the increased weight loss and body fat loss. This supports our findings by suggesting that the weight loss experienced was not only a result of a metabolic advantage, since there was a distinctly lower intake of calories as a result of less food intake, which created a negative energy balance.

Many nutrition scientists support the “calorie theory” and claim that a low-carbohydrate diet is not a healthy solution to losing weight. However, if we delve into a different facet of our study and examine how a high fat/low-carbohydrate diet affects the performance of individuals who exercise, we may find alternative results. Few studies have been done to observe the effects of a high fat/low-carbohydrate diet on obese individuals who are also exercising, or on how this diet affects endurance athletes. Since our study involved 100 obese subjects on the Atkins diet, and 100 on the conventional diet, both groups of which were we were following strict diet and exercise plans, we were able to examine this relationship.

When examining the results of those subjects participating in the high fat/low carbohydrate Atkins diet while exercising, we found that the subjects still lost weight and were able to perform exercise regularly or more often. Support for our findings can be found in a 1983 Phinney study, which indicated that obese subjects, engaging in moderate exercise while on a low-carbohydrate/high fat diet, could continue prolonged exercise at 60% of the their maximum volume of oxygen for a longer period of time. This maximum, or VO2MAX, indicates the level of oxygen being used in order to create muscle movement. At a level of 60%, the subjects exercise levels were high enough to allow their bodies to burn fat, rather than glycogen, thus improving their ability to continue exercise, since their bodies were low in carbohydrates but high in stored fat. Both studies indicate that, in the case of obese individuals, the Atkins diet can help to improve overall exercise performance and ability, if the exercise is of a moderate level, yet enough to force the body to use stored fat for energy.

In terms of the nutritional scientists’ claims that this type of diet is unhealthy, the studies above show that there can be healthful benefits to combining the Atkins diet with a light to moderate exercise program. Further proof of this can be seen, in part, by a Pogliaghi and Veicsteinas (1999) study, in which untrained, non-obese athletes were not found to be affected in terms of exercise performance by a low carbohydrate/high fat diet. This study, as well as our study, shows that while some individuals may not be affected by this type of diet in terms of exercise performance, and while some may benefit, it is unlikely that the diet will harm exercise performance. Since exercise is a part of any healthy lifestyle, this counterbalances the nutrition scientists’ claims that this type of diet is unhealthy.

One possible reason that the subjects in the Pogliaghi and Veicsteinas (1999) study did not appear to benefit from a low-carbohydrate/high fat diet might be that they have not been participating in endurance training. As an individual exercises, the resulting muscle contractions are done using ATP. How the body creates and uses this ATP is dependant upon the amount of the energy sources available, and the intensity and duration of the exercise. In all individuals, even those who are non-obese, glycogen is generally used for ATP and thus, during moderate exercise, the body creates ATP from available glycogen. As the intensity of exercise is increased, oxygen levels in the body decrease, which makes the creation of ATP difficult. The body, at this point, will begin to burn fat to substitute for this lack of ability. Since prolonged endurance training has the affect of conditioning the muscles to “crossover” to burn glycogen after longer time duration, trained individuals will burn more fat and less glycogen than untrained individuals will. This might explain why the study done by Pogliaghi and Veicsteinas (1999) yielded such results as it did, since the individuals in the study were not trained athletes.

As we look at studies done on the affect of low-carbohydrate / high fat diets on endurance athletes, we see a trend that this diet can be beneficial to these individuals, as well as the obese. In a study by Helge (et al., 1996), highly trained individuals were subjected to a workout that used 60 to 75% of the individuals’ VO2Max, and were found to benefit from a high fat/low carbohydrate diet. Since this VO2Max rate is one that would not cause the body to begin using glycogen as ATP in trained athletes, these findings are consistent with our previous results. In studies such as these, and the Phinney study, the results indicate that the benefits of a high fat / low carbohydrate diet depend on the physical state of the individual, and the intensity of the exercise. For obese individuals on the Atkins diet, a moderate exercise program that allows the body to burn fat rather than glycogen can be beneficial, since they would be able to exercise longer. For trained athletes, a higher level of exercise at a longer duration is possible, since the body’s threshold for the change to using glycogen as ATP is higher.

Thus, our results that obese individuals on that Atkins diet who participate in moderate activity are able to exercise for longer periods of time is supported.

In conclusion, our results indicated that weight loss in our subjects was caused from a negative energy balance, rather than metabolic advantage. The Atkins diet works well not because of a lowered carbohydrate intake, but because of a lowered overall food and caloric intake. This lower level of food intake in turn leads to a higher ratio between energy output, and energy intake. These results are further improved with the addition of moderate exercise, since the diet would improve overall exercise performance, and allow the body to burn more fat. Additionally, and for the same reasons, the Atkins diet would also serve highly trained athletes participating in endurance training.

Bibliography

Cecil, J.E., Francis, J., & Read, N.W. (1999, August). Comparison of the effects of a high-fat and high-carbohydrate soup delivered orally and intragastrically on gastric emptying, appetite, and eating behavior. Physiology and Behavior, 67(2), 299-306.

Freedman, M.R., King, J., & Kennedy, E. (2001, March). Popular diets: a scientific review. Obesity Research, 9(1), 40-47S.

Golay A, Allaz A-F, Morel Y, de Tonnac N, Tankova S, & Reaven G. (1996). Similar weight loss with low- or high-carbohydrate diets. American Journal of Clinical Nutrition, 63, 174-8.

Helge, J.W., Richter, E.A., & Kiens, B. (1996). Interaction of training and diet on metabolism and endurance during exercise in man. Journal of Physiology, 492, 293-306.

Holt, S.H., Delargy, H.J., Lawton, C.L., & Blundell, J.E. (1999, January). The effects of high carbohydrate vs. high fat breakfasts on feelings of fullness and alertness, and subsequent food intake. International Journal of Food Science Nutrition, 50(1), 12-28.

Phinney, S.D., Bristrian, B.R., Wolfe, R.R. & Blackburn, G.L. (1983, August). The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation. Metabolism, 32(8), 757-768.

Pogliaghi, S. & Veicsteinas, A. (1999, January). Influence of low and high dietary fat on physical performance in untrained males. Medicine & Science in Sports & Exercise, 31(1), 149-155.

References

1. Greene, L. & Gentile, C. (2002). Effects of low-carbohydrate diets and exercise on body weight and composition: A tutorial for IPHY 3700. University of Colorado-Boulder, unpublished manuscript.

2. McDonald, L. (1996).Atkins Diet Physiology: Metabolic or Not?

In this study, we examined the effects of a high fat/low-carbohydrate diet on body weight and composition, in comparison to the effects of a calorie-reduced, fat-restricted diet. We conducted this particular study in an effort to answer the question of whether weight loss occurs because of a metabolic advantage, where the body begins to use fat as energy due to a lowered carbohydrate intake, or because of a negative energy balance, where the energy expenditure of an individual is higher than the energy intake. Our findings suggest that weight loss occurs because of a negative energy balance, which supports other studies on calorie theory (Golay, et al., 1996; Freedman, et al., 2001).

By comparing the total daily calorie intake of subjects on the conventional diet to those on the Atkins diet, it was found that subjects on the Atkins diet achieved a greater reduction in calorie intake over the six-month study than subjects on the conventional diet (724 kcal/month Vs 496 kcal/month). In addition, body weight and overall body fat were also lower over the six-month period for those on the Atkins diet (16.2 kg & 8.1 Vs 10.8 kg & 5.2).

One possible explanation for these findings is that subjects on the Atkins diet may have experienced greater satiety, or satisfaction in relation to hunger, due to higher levels of fat content in the food sources designed for lower carbohydrate intake. A study by Cecil (et al., 1999) supports the concept that high-fat diets are more satiating than high carbohydrate meals. In the Cecil study, nine individuals were given high fat foods on one occasion and high carbohydrate foods on another occasion. Levels of satiety ratings were taken 2 hours after the meal, and the results showed that ingestion of high fat foods suppressed hunger and induced fullness more than the ingestion of high carbohydrate food.

It should be noted that in a 1999 study, Holt and his colleagues’ results contradicted those in this study and those in the Cecil study by claiming that a high-carbohydrate diet increased satiety. In the Holt study, fourteen participants were given four breakfasts on four random mornings, two of which consisted of high fat content, and two of which consisted of high carbohydrate content. Following the meal, participants left the research center, and recorded appetite and alertness ratings throughout the day. Holt interpreted the results to find that the high carbohydrate meals were more satiating than the high fat meals, and resulted in less food consumption during later meals for the subjects.

However, there was a flaw in the methods of Holt (et al., 1999). After the subjects ate their provided breakfasts at the research center, they were able to leave to continue normal day activities, including normal eating behaviors. Even Holt admits that subjects who consumed the high fat, low carbohydrate meal at the center may have simply gone back to normal eating habits of higher carbohydrates during the rest of day, which “may be a compensatory response to ingest a sufficient amount of food…to match the level of fullness produced by the subjects’ habitual breakfasts” (Holt, et al., 1999). In other words, the subjects may not have been reacting to levels of satiety, but rather, to habitual levels of food intake.

Our study did not restrict a calorie intake for the subjects on the Atkins diet, and yet the results showed these subjects actually achieved a greater reduction in calorie intake over the sixth month period, as well as a greater reduction in body fat and weight. This leads to the proposition that subjects on the Atkins diet chose to eat less food in their own, indicating that their high-fat, low carbohydrate diet increased feelings of satiety. This reduction in food in turn reduced their overall calorie intake, creating a negative energy balance. Since the subjects were isolated in a resort and were under strict observation, we can conclude that these individuals followed their diets accordingly, thereby eliminating the possibility that these individuals ate foods other that the high fat, low carbohydrate foods intended in the study. Additionally, we can discount the notion that the subjects may have been exercising, thus negating any possibility that higher levels of exercise were the cause of the increased weight loss and body fat loss. This supports our findings by suggesting that the weight loss experienced was not only a result of a metabolic advantage, since there was a distinctly lower intake of calories as a result of less food intake, which created a negative energy balance.

Many nutrition scientists support the “calorie theory” and claim that a low-carbohydrate diet is not a healthy solution to losing weight. However, if we delve into a different facet of our study and examine how a high fat/low-carbohydrate diet affects the performance of individuals who exercise, we may find alternative results. Few studies have been done to observe the effects of a high fat/low-carbohydrate diet on obese individuals who are also exercising, or on how this diet affects endurance athletes. Since our study involved 100 obese subjects on the Atkins diet, and 100 on the conventional diet, both groups of which were we were following strict diet and exercise plans, we were able to examine this relationship.

When examining the results of those subjects participating in the high fat/low carbohydrate Atkins diet while exercising, we found that the subjects still lost weight and were able to perform exercise regularly or more often. Support for our findings can be found in a 1983 Phinney study, which indicated that obese subjects, engaging in moderate exercise while on a low-carbohydrate/high fat diet, could continue prolonged exercise at 60% of the their maximum volume of oxygen for a longer period of time. This maximum, or VO2MAX, indicates the level of oxygen being used in order to create muscle movement. At a level of 60%, the subjects exercise levels were high enough to allow their bodies to burn fat, rather than glycogen, thus improving their ability to continue exercise, since their bodies were low in carbohydrates but high in stored fat. Both studies indicate that, in the case of obese individuals, the Atkins diet can help to improve overall exercise performance and ability, if the exercise is of a moderate level, yet enough to force the body to use stored fat for energy.

In terms of the nutritional scientists’ claims that this type of diet is unhealthy, the studies above show that there can be healthful benefits to combining the Atkins diet with a light to moderate exercise program. Further proof of this can be seen, in part, by a Pogliaghi and Veicsteinas (1999) study, in which untrained, non-obese athletes were not found to be affected in terms of exercise performance by a low carbohydrate/high fat diet. This study, as well as our study, shows that while some individuals may not be affected by this type of diet in terms of exercise performance, and while some may benefit, it is unlikely that the diet will harm exercise performance. Since exercise is a part of any healthy lifestyle, this counterbalances the nutrition scientists’ claims that this type of diet is unhealthy.

One possible reason that the subjects in the Pogliaghi and Veicsteinas (1999) study did not appear to benefit from a low-carbohydrate/high fat diet might be that they have not been participating in endurance training. As an individual exercises, the resulting muscle contractions are done using ATP. How the body creates and uses this ATP is dependant upon the amount of the energy sources available, and the intensity and duration of the exercise. In all individuals, even those who are non-obese, glycogen is generally used for ATP and thus, during moderate exercise, the body creates ATP from available glycogen. As the intensity of exercise is increased, oxygen levels in the body decrease, which makes the creation of ATP difficult. The body, at this point, will begin to burn fat to substitute for this lack of ability. Since prolonged endurance training has the affect of conditioning the muscles to “crossover” to burn glycogen after longer time duration, trained individuals will burn more fat and less glycogen than untrained individuals will. This might explain why the study done by Pogliaghi and Veicsteinas (1999) yielded such results as it did, since the individuals in the study were not trained athletes.

As we look at studies done on the affect of low-carbohydrate / high fat diets on endurance athletes, we see a trend that this diet can be beneficial to these individuals, as well as the obese. In a study by Helge (et al., 1996), highly trained individuals were subjected to a workout that used 60 to 75% of the individuals’ VO2Max, and were found to benefit from a high fat/low carbohydrate diet. Since this VO2Max rate is one that would not cause the body to begin using glycogen as ATP in trained athletes, these findings are consistent with our previous results. In studies such as these, and the Phinney study, the results indicate that the benefits of a high fat / low carbohydrate diet depend on the physical state of the individual, and the intensity of the exercise. For obese individuals on the Atkins diet, a moderate exercise program that allows the body to burn fat rather than glycogen can be beneficial, since they would be able to exercise longer. For trained athletes, a higher level of exercise at a longer duration is possible, since the body’s threshold for the change to using glycogen as ATP is higher.

Thus, our results that obese individuals on that Atkins diet who participate in moderate activity are able to exercise for longer periods of time is supported.

In conclusion, our results indicated that weight loss in our subjects was caused from a negative energy balance, rather than metabolic advantage. The Atkins diet works well not because of a lowered carbohydrate intake, but because of a lowered overall food and caloric intake. This lower level of food intake in turn leads to a higher ratio between energy output, and energy intake. These results are further improved with the addition of moderate exercise, since the diet would improve overall exercise performance, and allow the body to burn more fat. Additionally, and for the same reasons, the Atkins diet would also serve highly trained athletes participating in endurance training.

Bibliography

Cecil, J.E., Francis, J., & Read, N.W. (1999, August). Comparison of the effects of a high-fat and high-carbohydrate soup delivered orally and intragastrically on gastric emptying, appetite, and eating behavior. Physiology and Behavior, 67(2), 299-306.

Freedman, M.R., King, J., & Kennedy, E. (2001, March). Popular diets: a scientific review. Obesity Research, 9(1), 40-47S.

Golay A, Allaz A-F, Morel Y, de Tonnac N, Tankova S, & Reaven G. (1996). Similar weight loss with low- or high-carbohydrate diets. American Journal of Clinical Nutrition, 63, 174-8.

Helge, J.W., Richter, E.A., & Kiens, B. (1996). Interaction of training and diet on metabolism and endurance during exercise in man. Journal of Physiology, 492, 293-306.

Holt, S.H., Delargy, H.J., Lawton, C.L., & Blundell, J.E. (1999, January). The effects of high carbohydrate vs. high fat breakfasts on feelings of fullness and alertness, and subsequent food intake. International Journal of Food Science Nutrition, 50(1), 12-28.

Phinney, S.D., Bristrian, B.R., Wolfe, R.R. & Blackburn, G.L. (1983, August). The human metabolic response to chronic ketosis without caloric restriction: physical and biochemical adaptation. Metabolism, 32(8), 757-768.

Pogliaghi, S. & Veicsteinas, A. (1999, January). Influence of low and high dietary fat on physical performance in untrained males. Medicine & Science in Sports & Exercise, 31(1), 149-155.

References

1. Greene, L. & Gentile, C. (2002). Effects of low-carbohydrate diets and exercise on body weight and composition: A tutorial for IPHY 3700. University of Colorado-Boulder, unpublished manuscript.

2. McDonald, L. (1996). The ketogenic diet: A complete guide for the dieter and practitioner: Physiology of ketosis chapters. Kearney, Nebraska: Morris Publishing.

3. Samaha et al. (2003). A low-carbohydrate as compared with a low-fat diet in severe obesity. The New England Journal of Medicine, 348, 2074-2081.

4. Helge, J.W., Richter, E.A., & Kiens, B. (1996). Interaction of training and diet on metabolism and endurance during exercise in man. Journal of Physiology, 492, 293-306.

5. Lambert, E.V., Speechly, D.P., Dennis, S.C., & Noakes, T.D. (1994). Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet. European Journal of Applied Physiology, 69, 287-293.

6. Muoio, D.M., Leddy, J.J., Horvath, P.J., Awad, A.B., & Pendergast, D.R. (1994). Effect of dietary fat on metabolic adjustments to maximal VO2 and endurance in runners. Medicine and Science in Sports and Exercise, 26, 81-88.: A complete guide for the dieter and practitioner: Physiology of ketosis chapters. Kearney, Nebraska: Morris Publishing.

3. Samaha et al. (2003). A low-carbohydrate as compared with a low-fat diet in severe obesity. The New England Journal of Medicine, 348, 2074-2081.

4. Helge, J.W., Richter, E.A., & Kiens, B. (1996). Interaction of training and diet on metabolism and endurance during exercise in man. Journal of Physiology, 492, 293-306.

5. Lambert, E.V., Speechly, D.P., Dennis, S.C., & Noakes, T.D. (1994). Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet. European Journal of Applied Physiology, 69, 287-293.

6. Muoio, D.M., Leddy, J.J., Horvath, P.J., Awad, A.B., & Pendergast, D.R. (1994). Effect of dietary fat on metabolic adjustments to maximal VO2 and endurance in runners. Medicine and Science in Sports and Exercise, 26, 81-88.