Many believe that the Paleolithic “ketogenic diet” may be the answer for a healthier life, and for increased performance and weight loss during sport and physical activities. A study by Paoli, et al. observed that when elite male gymnasts were placed on a very low carbohydrate “ketogenic” diet they were able to decrease weight and fat mass without seeing a decrease, or increase in physical performance (1). This paper supports that a very low carbohydrate diet, or “ketogenic” diet, supports weight loss in athletes by decreasing fat mass, but does not enhance athletic performance.
Paoli, et al. included 8 male gymnasts as participants. This study used an experimental design where participants acted both as control group and the group receiving the treatment. The researchers found that after 30 days on a very low carbohydrate diet there was a significant decrease in average body weight from 153 pounds to 149.6, or approximately 4.6 pounds (p-value = <0.05). Fat mass also decreased from 11.6 pounds to 7.5 pounds for a decrease of approximately four pounds (p-value = <0.001), and the researchers suggested that all of the weight loss during the 30 day period was from fat mass. Athletes did not see a significant decrease or increase in athletic performance while on the very low calorie diet (1).
This was not a very strong study because of the small sample size. The participants also acted as the control group, while consuming a typical American or “western” diet for 30 days. There was a 3 month wait period, and then the athletes consumed a very low carbohydrate diet for 30 days while maintaining the same exercise routine as the first 30 days. For a strong study, it would have been better to have separate participants for the control group. There are many possible confounding factors for this study. Athletes may have worked out harder during the second 30 day period because they were months farther into their conditioning. This study also only followed the short term effects of a very low carbohydrate diet and physical performance. Long term effects of a very low carbohydrate diet include: dehydration, gastrointestinal symptoms, low blood sugar, carnitine and vitamin deficiencies, hypeplipidemia or high fat in the blood, impaired cognitive function, osteoporosis, and the potential for arthritic and kidney problems, and the list of negative side effects continues further than those listed (2). There were not any notable strengths to this study.
In the same study by Paoli et al. they found that comparing non-ketogenic with ketogenic low-calorie diets aiming for weight loss over a month period did not show any statistical difference of one diet having an advantage over the other for weight loss. They concluded that lower energy intake, rather than low carbohydrate intake is the key to losing weight, (2) so the focus should be removed from low carbohydrate diets, to low calorie diets. For athletic performance, in the opinion of most doctors and nutrition experts, carbohydrates must compose of a large portion of one’s daily energy intake if optimum performance is desired to be maintained (3). With this in mind, it would be difficult to maintain physical performance long-term on a very low carbohydrate diet. In another study testing athlete’s maximal power output on a bicycle for 30 second bouts, the researcher found that following a very low carbohydrate diet reduced their average maximal power output (4). This study found that the very low carbohydrate diet had a negative effect on physical performance, which contradicts the results of the study by Paoli where the very low carbohydrate diet had neither a positive or negative effect on physical performance.
In conclusion, this was a weak study and the findings from it should be taken with caution. A very low carbohydrate “ketogenic” diet may produce weight loss in a short term setting, but for a long term weight loss program, the negative side effects would far outweigh the benefits of this diet. There are mixed results about whether a very low carbohydrate diet negatively affects physical performance. There is not much research in this field to compare other studies to Paoli, or to support the trending Paleolithic “ketogenic” diet. Consumers should not rely on a very low carbohydrate diet for a weight loss option while competing in sports or strictly for a long term weight loss program.
- Paoli, A., Grimaldi, K., D’Agostino, D., Cenci, L., Moro, T., Bianco, A., & Palma, A. (2012). Ketogenic diet does not affect strength performance in elite artistic gymnastics. Journal of the International Society of Sports Nutrition. 9(34), 1-9.
- Bilsborough, S.A., & Crowe, T.C. (2003). Low-carbohydrate diets: what are the potential short- and long-term health implications? Asia Pacific J Cin Nutr, 12(4), 396-404.
- Phinney, S.D. (2004). Ketogenic diets and physical performance. Nutrition and Metabolism,1(2), 1-7.
- Langfort, J., Zarzecny, R., Nazar, K., & Kaciuba-Uscitko, H. (1997). The effect of low carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise. Eur J Appl Physiol,(76), 128-133.
Reviewed by Viktoriya Wolff