Calorie Hypothesis of Obesity
Everyone knows starvation makes you thin and overeating makes you fat and the “calorie in calorie out” theory of weight control is at the heart of nutritional advice and food labelling, nevertheless for many reasons counting calories usually fails over the long term. Calorie restriction no doubt has health benefits but a lifetime of hunger is not likely to catch on with most people. We eat food not calories and there are staggering numbers of possible food combinations to choose that can have distinct effects on appetite, physiological responses and cell signaling. There are physical limitations to consuming plant foods with high fiber and water content (1) and there is evidence to suggest hunger is accentuated when attempting calorie restriction with diets containing high glycemic filler foods like bread, potatoes, rice, pasta, flour and sugar as opposed to high fiber (2) and ketogenic diets (3) (4) (5)
On the other side of the equation calories out is equally complicated with physical activity, heat generation, work of metabolism, growth and development, healing processes, calorie losses in faeces and urine all having significant effects.
Exercise is a highly beneficial activity but the impact of exercise on “calories out” is commonly overestimated, and exercise alone is unlikely to reverse obesity unless you put in the sort of time required of professional athletes. For instance resting energy expenditure is typically 100 Calories per hour and the most vigorous exercise would expend 10 times that figure while moderate exercise increases to 3 to 4 times resting metabolic rate, so that 30 minutes of moderate exercise results in additional calories out of around 150 Cals the equivalent of 17 gms of fat.
Faecal loss of calories is frequently underestimated particularly so with increased faecal output from high fiber consumption (6). Calorie content of faeces is around 2 Cals per gm (7) and the typical low fiber Western Diet (10-15 gms/d) might be associated with a faecal output of 100 g/day and this could rise to 200-400 g/d with recommended (35 g/d) or even higher fiber intakes (6) which may result in faecal calorie output of between 400 and 800 Cals/day. Studies have indicated a 1 g/d increase in fiber results in a 5 gm/d increase in stool weight but of that the calorie content, particularly from fat, increases proportionately more (8).
Resting energy expenditure varies considerably with stages in life; proportionately much higher with growth and development, levelling off in adulthood and progressively declining with age. There is a well-known thermal effect of foods whereby energy expenditure increases after meals proportionately with calorie content although, in experimental rodents a ketogenic diet increases oxygen consumption and causes weight loss in spite of increased calorie intake (9) although this has not been clearly demonstrated in human studies there are mechanisms related to energy uncoupling through fatty acid metabolism and up-regulation of uncoupling proteins to explain how these things might happen. In addition, there have been many studies comparing unrestricted ketogenic diets with calorie restricted low fat diets for weight loss and most have shown greater weight loss with ketogenic diets despite higher calorie intake (10) (11) (1).
1. D J A Jenkins, J M Wong, CWC Kendall, A Esfahani, T Leong, DA Faulkner, E Vidgen, KA Greaves, G Paul, W Singer. The effect of a Plant based low carbohydrate (ECO-Atkins) diet of body weight and blood lipid concentrations in hyperlipidemic subjects. s.l. : Arch Intern Med 169: 11 June 8, 2009 1046-1054, 2009.
2. Elin V Johansson, Anne C Nilsson, Elin M Östman and Inger M E Björck . Effects of indigestible carbohydrates in barley on glucose metabolism, appetite and voluntary food intake over 16 h in healthy adults. . s.l. : Nutrition Journal 2013, 12:46.
3. P Sumithran, LA Prendergast, E Delbridge, K Purcell, A Shulkes, A Kriketos, J Proietto. Ketosis and appetite-mediating nutrients and hormones after weight loss. . s.l. : European Journal of Clinical Nutrition (2013) 67, 759–764; doi:10.1038/ejcn.2013.90;.
4. Margriet A. B. Veldhorst1, Klaas R. Westerterp, Anneke J. A. H. van Vught, Margriet S. Westerterp-Plantenga. Presence or absence of carbohydrates and the proportion of fat in a high-protein diet affect appetite suppression but not energy expenditure in normal-weight human subjects fed in energy balance. s.l. : British Journal of Nutrition 2010: 1-11 doi:10.1017/S000711451000206.
5. SCHARRER, ERWIN. Control of Food Intake by Fatty Acid Oxidation and Ketogenesis. . s.l. : Nutrition Vol. 15, No. 9, 1999.
6. K. L. Wrick, J. B. Robertson, P. J. Van Soest, B. A. Lewis, J. M. Rivers, D. A. Roe, L. R. Hackler. The Influence of Dietary Fiber Source on Human Intestinal Transit and Stool Output. . s.l. : J. Nutr. 113: 1464-1479, 1983.
7. J L Murphy, S A Wootton, S A Bond, A A Jackson. Energy content of stools in normal healthy controls and patients with cystic fibrosis. . s.l. : Archives of Disease in Childhood 1991; 66: 495-500.
8. Hsiao-Ling Chen, Valerie S Haack, Corey W Janecky, Nicholas W Vollendorf, Judith A Marlett. Mechanisms by which wheat bran and oat bran increase stool weight in humans. . s.l. : Am J Clin Nutr 1998;68:711–9.
9. Adam R. Kennedy, Pavlos Pissios, Hasan Otu, Bingzhong Xue, Kenji Asakura, Noburu Furukawa, Frank E. Marino, Fen-Fen Liu, Barbara B. Kahn, Towia A. Libermann, Eleftheria Maratos-Flier. A high-fat, ketogenic diet induces a unique metabolic state in mice. s.l. : Am J Physiol Endocrinol Metab 292:E1724-E1739, 2007. First published 13 February 2007;.
10. Jeff S Volek, Richard D Feinman. Carbohydrate restriction improves the features of Metabolic Syndrome: Metabolic Syndrome may be defined by the response to carbohydrate restriction. s.l. : Nutrition & Metabolism 2005: 2:31, 2005.
11. Eric C Westman, William S Yancy Jr, John C Mavropoulos, Megan Marquart and Jennifer R McDuffie. The effect of a low-carbohydrate, ketogenic diet versus a low fat diet to treat type 2 diabetes. s.l. : Nutrition & Metabolism 2008 5:36, 2008.