Letter to the Editor by Javier T. Gonzalez, Research Fellow, Department for Sport, Health & Rehabilitation, Northumbria University, Newcastle-upon-Tyne, UK
The editorial by Brukner  provokes an interesting debate around two nutrition-related principles that are certainly worth of discussion. There are however, some points that may be misleading to some readers, particularly regarding the second point. The major problem is the oversimplification of complex issues, which begins in the description of the “principle”: “The optimum diet for weight control, general health and athletic performance consists of low fat, high carbohydrate” . The diet for athletic performance is clearly possible to differ from a diet optimized for weight control and/or general health.
Carbohydrate restricted diets are certainly efficacious in weight control and for improving some markers of metabolic health such as triacylglycerol and high-density lipoprotein concentrations . With regards to primary end points, a Mediterranean-style diet including high intakes of extra-virgin olive oil and nuts reduced the incidence of cardiovascular events by ~30% compared to a low fat diet (which as a result was relatively high-carbohydrate) . Changing the focus from reducing fat intake to focusing on evidence-based diet patterns such as the Mediterranean diet would be a positive step, however, this does not support a role for a very-low-carbohydrate diet.
Dr Brukner refers to the appetite effects of macronutrients and intriguingly states that: “advocates of the high fat diet emphasise that fats (and to a lesser extent protein) are satiating” . This statement is not supported by a reference. In fact, evidence points to the contrary. Protein is generally found to be the most satiating macronutrient, with spontaneous energy intake falling when protein replaced with fat or carbohydrate in the diet [4 5]. High fat intake, can lead to overconsumption due to the high energy density of fat [6 7]. Another erroneous point is that insulin is only stimulated by carbohydrate. Protein is well-known to produce an insulin response . It is unfortunate that this evidence has been neglected.
A related point is that circulating ketone body concentrations, which rise in response to low carbohydrate availability (achieved by carbohydrate restriction and/or exercise, in the presence or absence of high-fat intake), suppress appetite . A potential concern however, with diets that severely restrict carbohydrate is the limited fibre intake. This likely has broad implications for gut microbiome , the consequences of which may include immune, appetite, inflammatory and metabolic effects that are not likely to be conducive to health.
Brukner also makes that statement: “glycogen, the storage form of carbohydrate, was thought to be a more efficient fuel than fat. This has also been challenged of late by scientists who argue that fat provides more calories per gram and also has much larger body stores” . Each individual point made in this statement is correct and, although Brukner proposes that they conflict with one another, they do not. Almost 100 y ago carbohydrate was shown to be a more efficient fuel during exercising humans , that is, less oxygen is consumed per kJ of work done. This is a separate point to the fat providing more energy per unit mass or that humans’ capacity to store energy as fat is greater that carbohydrate. These points are not debated against, however, this statement manufactures otherwise preventable confusion.
The statement that: “Noakes argues that after a week or two of carbohydrate deprivation, our bodies change from a carbohydrate metabolism to a fat metabolism with health and performance improvements”  sounds as if this is a novel concept. It has been known for almost a century that manipulation of carbohydrate and fat in the diet influences fuel metabolism during exercise . What has never been shown, to the authors knowledge however, is that a high-fat diet improves performance in a performance trial that mimics “real-world” conditions with high pre- exercise glycogen concentrations. In fact, when fat metabolism is upregulated with a high-fat diet, this suppresses pyruvate dehydrogenase activity  and thus carbohydrate metabolism is downregulated along with decrements in the capacity to perform high-intensity exercise .
A major issue with high-fat vs. high-carbohydrate diets is the unnecessary polarization and oversimplification of an complex issue. Periodisation of macronutrient intake may be a useful strategy for endurance athletes  and carbohydrate/food intake can be restricted at certain times of the day to manipulate metabolism and appetite [15 16]. Whilst the public may benefit from reducing their carbohydrate intake (particularly refined and processed carbohydrates and sugars), a focus on changing dietary patterns (such as the Mediterranean diet) can achieve this along with other effects that are likely beneficial including intakes of beneficial compounds consumed in the food matrix and context that is most suitable for health. Very low carbohydrate intakes are not likely beneficial for all aspects of health and many athletes would certainly benefit from a high-carbohydrate diet for prolonged periods of their season. Perhaps we should remember that the athlete and the general population are very different models with different goals and that we should consider carbohydrate and fat availability (ie. intake and expenditure) as an excess of either is detrimental. A further degree of complexity is apparent upon consideration of lifestyle of the individual. A high energy turnover offers some protection of metabolic health over low energy turnover even in the presence of similar degrees of energy surplus .
1. Brukner P. Challenging beliefs in sports nutrition: are two ‘core principles’ proving to be myths ripe for busting? British Journal of Sports Medicine, 2013;47(11):663-64.
2. Nordmann AJ, Nordmann A, Briel M, et al. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta- analysis of randomized controlled trials. Archives of internal medicine 2006;166(3):285-93 doi: 10.1001/archinte.166.3.285[published Online First: Epub Date]|.
3. Estruch R, Ros E, Salas-Salvado J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013;368(14):1279-90 doi: 10.1056/NEJMoa1200303[published Online First: Epub Date]|.
4. Martens EA, Lemmens SG, Westerterp-Plantenga MS. Protein leverage affects energy intake of high-protein diets in humans. Am J Clin Nutr 2013;97(1):86-93 doi: 10.3945/ajcn.112.046540[published Online First: Epub Date]|.
5. Weigle DS, Breen PA, Matthys CC, et al. A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. Am J Clin Nutr 2005;82(1):41-8.
6. Lissner L, Levitsky DA, Strupp BJ, et al. Dietary fat and the regulation of energy intake in human subjects. American Journal of Clinical Nutrition 1987;46(6):886-92.
7. Stubbs RJ, Harbron CG, Murgatroyd PR, et al. Covert manipulation of dietary fat and energy density: effect on substrate flux and food intake in men eating ad libitum. American Journal of Clinical Nutrition 1995;62(2):316-29.
8. Nilsson M, Stenberg M, Frid AH, et al. Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins. Am J Clin Nutr 2004;80(5):1246-53.
9. Johnstone AM, Horgan GW, Murison SD, et al. Effects of a high-protein ketogenic diet on hunger, appetite, and weight loss in obese men feeding ad libitum. Am J Clin Nutr 2008;87(1):44-55.
10. David LA, Maurice CF, Carmody RN, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 2013 doi: 10.1038/nature12820[published Online First: Epub Date]|.
11. Krogh A, Lindhard J. The Relative Value of Fat and Carbohydrate as Sources of Muscular Energy: With Appendices on the Correlation between Standard Metabolism and the Respiratory Quotient during Rest and Work. The Biochemical journal 1920;14(3-4):290-363
12. Stellingwerff T, Spriet LL, Watt MJ, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol Endocrinol Metab 2006;290(2):E380-8 doi: 10.1152/ajpendo.00268.2005[published Online First: Epub Date]|.
13. Havemann L, West SJ, Goedecke JH, et al. Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance. J Appl Physiol (1985) 2006;100(1):194-202 doi: 10.1152/japplphysiol.00813.2005[published Online First: Epub Date]|.
14. Stellingwerff T. Case study: nutrition and training periodization in three elite marathon runners. Int J Sport Nutr Exerc Metab 2012;22(5):392- 400.
15. Yeo WK, Paton CD, Garnham AP, et al. Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J Appl Physiol (1985) 2008;105(5):1462-70 doi: 10.1152/japplphysiol.90882.2008[published Online First: Epub Date]|.
16. Gonzalez JT, Veasey RC, Rumbold PL, et al. Breakfast and exercise contingently affect postprandial metabolism and energy balance in physically active males. British Journal of Nutrition 2013;110(4):721-32 doi: 10.1017/S0007114512005582[published Online First: Epub Date]|.
17. Walhin JP, Richardson JD, Betts JA, et al. Exercise counteracts the effects of short-term overfeeding and reduced physical activity independent of energy imbalance in healthy young men. J Physiol 2013;591(Pt 24):6231-43 doi: 10.1113/jphysiol.2013.262709[published Online First: Epub Date]|.