In the sports nutrition realm food is fuel, and more is generally better. But could a ‘less is more’ approach pay off on the track?

Reducing energy intake, ie; ‘calorie restriction’, comes in many forms from the 5-2 diet, OMAD, intermittent fasting, every other day fasting or even prolonged fasting. The act of cutting calories has been associated with a wide variety of benefits including; Increase lifespan, Delays onset of related diseases, Increased immune function, Decreased insulin sensitivity, Resistance to stressors such as heat, metabolic and oxidative, Regulates body weight and much more.

One place we don’t usually associate calorie restriction however is sports performance, where the prevailing message is to fuel, not deprive. And yet optimal body composition and overall health can provide a significant competitive advantage. So, is there a place for caloric restriction when it comes to athletic performance?

A paper published in the journal of the international society of sports nutrition set out to answer this question. A team of researchers recruited 12 male Olympic athletes and every other day for a total of 6 weeks, reduced their caloric intake by 30-40% whilst evaluating markers of physical performance. Participants engaged in a balanced diet prior to the intervention and were physically active 3-6 times per week. Normal calorie intake averaged 2350, with fasting days coming in at around 1537 calories.

Athletes were subjected to an incremental treadmill test, running to exhaustion, at the beginning and end of the intervention as well as after every fasting day. By the end of the study athletes were able to perform the same exercise and intensity with lower heart rate, and energy expenditure was 10% lower after the intervention, indicating athletes had a more efficient use of energy.

Throughout the study, regular blood samples were also taken to analyse the nutritional status of the athletes. Researchers observed reduced oxidative damage, as well as reduced circulating triglyceride and cholesterol levels. Although calories were cut, overall macronutrient split appeared similar on both fasting and non fasting days. On fasting days, micronutrient intake was unsurprisingly reduced, and whilst this resulted in daily intakes below that of the RDA for athletes in a range of vitamins and minerals, blood markers of the nutritional status of the athletes remained the same before and after the study.

Although these short term ‘deficiencies’ did not appear to cause any adverse effects over the the intervention period, it is worth noting that following this calorie restrictive diet longer term, without supplementation, could ameliorate the positive effect on performance.

With regards to body composition, fat mass was reduced by an average of 15.1% and total body water was reduced by 2.5kg. Researchers also saw a reduction of lean body mass, (2.91%) and suggested that this may have be prevented by addressing the macronutrient split, increasing protein intake to around 2.3g/kg of body weight, or supplementing with branched chain amino acids in order to aim to preserve lean mass. Whilst loss of lean mass is usually seen as a negative in the fitness industry, the researchers postulated that because this decrease wasn’t accompanied by an impairment of physical performance, this may indicate that athletes could have an ‘ideal lean body mass’ for peak performance and higher muscle mass does not necessarily indicate better athletic results.

Lastly, Blood tests confirmed lactate levels during running were significantly lower after the 6-week intervention period. Blood lactate levels increase with exercise and serve as a marker of muscle fatigue, so a lower score at the end of the study indicates muscles are able to perform the same exercises for longer before exhaustion.

Whilst this paper makes a compelling argument for the use of calorie restriction in an athletic setting, there are some things to bear in mind; firstly, the sample size is very small, and all males. Previous studies have indicated there are gender differences with regards to how the body handles fasting

There is also the potential to become deficient in a wide range of nutrients as well as lean mass loss if the protocol is followed for a significant amount of time. This model of calorie restriction for performance might be best followed as a short-term plan (for instance as a run up to a race) as opposed to a longer-term lifestyle approach. As the study only followed participants for 6 weeks, we have no indication whether performance continues to increase after this time or perhaps starts to decline due to muscle mass loss.

The topic area of fasting, and its effect on a variety of health parameters, is emerging as an exciting research area. And whilst there seems to be many benefits touted to calorie restriction, the subject is still in its infancy, so caution and common sense should be applied to any individual looking to engage in fasting for performance.