Diet and weight loss
====================

* Anssi Manninen

Irene Strychar's recent review of diet in the management of weight loss1 contains some incorrect and biased statements. For example, according to the author, during very-low-carbohydrate intake, “the body depletes its glycogen stores, and gluconeogenesis is induced, whereby lean tissue is used to produce glucose as an energy source for the brain.” This statement is clearly fallacious. True, animals share the metabolic deficiency of the total (or almost total) inability to convert fatty acids to glucose. Thus, the primary substrate for gluconeogenesis is amino acid, with some help from glycerol (obtained from fat tissue triglycerides). However, when the rate of mobilization of fatty acids from fat tissue is accelerated, as, for example, with a very-low-carbohydrate diet, the liver produces ketone bodies. The liver cannot use these ketone bodies, which therefore flow from the liver to extrahepatic tissues (e.g., brain, muscle) for use as a fuel. Simply stated, ketone body metabolism by the brain displaces glucose utilization and thus spares muscle mass. In other words, the brain derives energy from storage fat during consumption of a very-low-carbohydrate diet.

Numerous studies indicate that a diet low in carbohydrate and high in protein is, if anything, protective against loss of muscle mass during energy restriction.2–4 This topic is covered in detail in 2 recent reviews.5,6

## REFERENCES

1.  1. Strychar I. Diet in the management of weight loss. CMAJ 2006;174(1):56-63.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czo4OiIxNzQvMS81NiI7czo0OiJhdG9tIjtzOjI0OiIvY21hai8xNzUvMTEvMTQwNy4xLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

2.  2. Young CM, Scanlan SS, Im HS, et al. Effect of body composition and other parameters in obese young men of carbohydrate level of reduction diet. Am J Clin Nutr 1971;24:290-6.
    
    [Abstract](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiYWpjbiI7czo1OiJyZXNpZCI7czo4OiIyNC8zLzI5MCI7czo0OiJhdG9tIjtzOjI0OiIvY21hai8xNzUvMTEvMTQwNy4xLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

3.  3. Willi SM, Oexmann MJ, Wright NM, et al. The effects of a high-protein, low-fat, ketogenic diet on adolescents with morbid obesity: body composition, blood chemistries, and sleep abnormalities. Pediatrics 1998;101:61-7.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MTA6InBlZGlhdHJpY3MiO3M6NToicmVzaWQiO3M6ODoiMTAxLzEvNjEiO3M6NDoiYXRvbSI7czoyNDoiL2NtYWovMTc1LzExLzE0MDcuMS5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=) 

4.  4. Volek JS, Sharman MJ, Love DM, et al. Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism 2002;51:864-70. 
    
    [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.1053/meta.2002.32037&link_type=DOI) 
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=12077732&link_type=MED&atom=%2Fcmaj%2F175%2F11%2F1407.1.atom) 
    
    [Web of Science](http://www.cmaj.ca/lookup/external-ref?access_num=000176578200011&link_type=ISI) 

5.  5. Manninen AH. Is a calorie really a calorie? Metabolic advantage of low-carbohydrate diets. J Int Soc Sports Nutr 2004;1(2):21-6.
    
    

6.  6. Manninen AH. Very-low-carbohydrate diets and preservation of muscle mass. *Nutr Metab (Lond)* 2006;3:9.