Carborexia Nervosa

Carborexia Nervosa

“An irrational fear of carbohydrate” spread by tabloid journalists and ill-informed personal trainers. From a sport nutrition or strength and conditioning perspective, carbohydrate restriction would cost trophies. A low carbohydrate diet would likely have a negative impact on your physique and wellbeing too. Hopefully I don’t need to point out that I’m not talking about pizzas here. Rather, low glycemic carbohydrate sources such as oats, rice, vegetables and fruit. Whilst its widely accepted that carbohydrate is beneficial for endurance, this macronutrient also plays an integral role in fuelling demanding resistance training sessions, improving cognition and increasing hormone production.

The breakdown of carbohydrate for fuel (a process called glycolysis) accounts for 82 % of the energy we use when lifting weights according to a classic study published in the Journal of Applied Physiology (MacDougall et al., 1977). It stands to reason that if our carbohydrate stores are running on fumes, our physical performance will be compromised. The Journal of Strength and Conditioning Research reported that carbohydrate restriction had a negative impact on training volume, with squat performance deteriorating significantly by set three (Leveritt and Abernethy, 1999). To improve your body composition (the ratio of fat to muscle) you need to preserve as much muscle as you can whilst you lose fat. In addition to sufficient protein intake, resistance training will be the key tool in minimising this undesired atrophy. To maintain muscle mass in a calorie deficit, you need to dramatically increase the total volume of work done within each of session. More reps per set, more sets per exercise, reduced rest intervals. Carbohydrate will be essential in fuelling this increased workload.

How much carbohydrate do you need? A review of the literature suggests that competitive bodybuilders (from national to world-class level) consume between 4-5 g carbohydrate per kg bodyweight per day (Slater and Phillips, 2013). The ratio is roughly 2:1 carbohydrate to protein, and between 37-48 % of total calories. Females require slightly less proportionate to their (generally) smaller bodyweight (Volek et al., 2006).

Do we need to move away from promoting protein-dominant diets? Whilst protein has many well-documented benefits for muscle gain and fat loss, exceeding the upper limit bestows no further advantage. Worryingly, The American Journal of Clinical Nutrition reported that excessive protein intake actually increases protein catabolism (Moore et al., 2009). Take a look at the Advance Coaching Academy’s review of the latest protein literature for detailed recommendations on intake and meal frequency:

We’ve discussed physical performance, but what about cognition? The brain only weighs 2 % of our total bodyweight, yet uses 20 % of the body’s energy (at rest). Energy requirements are met exclusively through glucose. Yet the brain has a poor capacity for storage. Without replacement, the brain would be depleted of glucose in less than 10-minutes (Benton and Parker, 1998). But don’t worry as almost all carbohydrate eaten, with the exception of fibre, is converted to glucose. A recent study published in the Journal of Neurology and Neuroscience, reported that the brain oxidises between 100-120 g of glucose over 24-hours (White et al., 2018). Based on this research, I’d suggest this as the minimum. The impact of calorie-matched lunches containing varying amounts of carbohydrate on cognitive performance and wellbeing were scrutinised by Lloyd and his colleagues (1990). Participants who ate a low carbohydrate lunch (24 % carbohydrate)
reported being more drowsy, muddled and less cheerful than those who a medium carbohydrate lunch (42 % carbohydrate).

Lastly, when calories and dietary fat are the same, testosterone levels are consistently higher in men consuming a high carbohydrate diet, as opposed to a high protein intake. Anderson et al. (1987) reported that testosterone was 28 % higher in men consuming a carbohydrate-rich diet containing foods such as vegetables and fruit. As an added bonus, cortisol concentrations were between 14 and 64 % lower in the high carbohydrate group.

Written by ACA Contributor Jason Jackson

Jason’s career began in 2008 when he joined an experienced personal training team at a Virgin Active health club in Northwest London. By 2012 Jason had become an accredited strength and conditioning coach, giving him the necessary credentials to work with professional athletes. Jason spent a season at Brentford Football Club, before a further two-years conducting research at the Saracens’ human performance lab.

In 2017 Jason became a Master of Science in sport nutrition. For his thesis, Jason spent two-years conducting a systematic review of over 100 testosterone studies. In addition to the well-documented physical effects on muscle mass and body fat, Jason examined testosterone’s significant influence on cognitive performance and wellbeing. Jason then integrated his findings into a unified strategy to successfully reverse the age-related decline in testosterone.

Jason is a registered nutritionist with SENr, the performance-orientated division of the British Dietetic Association. In his role as educator, Jason delivers seminars on performance and wellbeing at corporate accounts across the City of London. Clients include All Saints, RBS and exclusive high-end members club The Ned. The number one trainer in Virgin Active’s 20-year history, Jason wrote the book (literally) on nutrition strategy for the company.



1. Anderson, K.E., Rosner, W., Khan, M.S., New, M.I., Pang, S., Wissel, P.S. and Kappas, A., 1987. Diet-hormone interactions: protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man.Life sciences, 40(18), pp. 1761-1768.

2. Benton, D. and Parker, P.Y., 1998. Breakfast, blood glucose, and cognition.The American journal of clinical nutrition, 67(4), pp.772S-778S. Leveritt, M. and Abernethy, P.J., 1999. Effects of carbohydrate restriction on strength performance.The Journal of Strength & Conditioning Research, 13(1), pp.52-57.

3. Lloyd, H.M., Green, M.W. and Rogers, P.J., 1994. Mood and cognitive performance effects of isocaloric lunches differing in fat and carbohydrate content. Physiology & behavior, 56(1), pp.51-57.

4. MacDougall, J.D., Ward, G.R. and Sutton, J.R., 1977. Muscle glycogen repletion after high-intensity intermittent exercise.Journal of Applied Physiology, 42(2), pp.129-132.

5. Moore, D.R., Robinson, M.J., Fry, J.L., Tang, J.E., Glover, E.I., Wilkinson, S.B., Prior, T., Tarnopolsky, M.A. and Phillips, S.M., 2008. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men.The American journal of clinical nutrition, 89(1), pp.161-168.

6. Slater, G. and Phillips, S.M., 2013. Nutrition guidelines for strength sports: sprinting, weightlifting, throwing events, and bodybuilding. In Food, Nutrition and Sports Performance III(pp. 75-86). Routledge. Volek, J.S., Forsythe, C.E. and Kraemer, W.J., 2006. Nutritional aspects of women strength athletes. British journal of sports medicine, 40(9), pp. 742-748.

7. White, H., Venkatesh, K. and Venkatesh, B., 2018. Systematic Review of the Use of Ketones in the Management of Acute and Chronic Neurological
Disorders. J Neurol Neurosci, 8, p.2.