Letter to the Editor by Javier T. Gonzalez, Research Fellow, Department for Sport, Health & Rehabilitation, Northumbria University, Newcastle-upon-Tyne, UK
IN RESPONSE TO: 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.
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 .
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