Intermittent fasting - two sides to the story…

Intermittent fasting (IF) has been scientifically claimed to improve several health indices, including insulin sensitivity, weight management, inflammation, oxidative stress, cardiovascular health, and the detoxification of cellular waste. All of these observations make absolute sense to me because the digestion of food is a metabolically energy demanding job, requiring strong input from pretty much every biological system in our body.

So, an intermittent break from eating is not a bad idea - I particularly like to rest my gastrointestinal tract from time to time, as it also lowers detox requirements, quietens down the pancreas (insulin) and diminishes cellular inflammation and ageing - for a while at least…

However, whenever there is such a strong and prevailing scientific health message such as this one on intermittent fasting, I always ask an incredibly simple, but important question: “What is the other side of the story?”

From a general health perspective, assuming we are eating nutrient-rich food, the food we might be cutting back on during IF, is the same food that provides the micro-nutrition needed to turn over our vital physiological processes. To take one example, B-vitamins (available from a wide variety of whole foods) are vital for: insulin receptor sensitivity, detoxification, mitochondrial energy production, methylation, adrenal support, and neurotransmitter production. Many of us consume a diet that is relatively low in many essential micronutrients, so if we are to remove one meal per day during an IF regime, we’d better make very good dietary choices at the other sittings! Of course, many of our athletes eat an extremely processed, sugary and inflammatory diet, so in such cases, we would expect the person to make some substantial health gains with IF, and this is one important reason for the regime’s success - perhaps we could become even healthier simply by eating better quality food?

Within this enquiry about IF, let’s now consider athletes specifically. The Team Sky nutritionist Dr James Morton, from Liverpool John Moores University, has done quite a bit of research on low-carb and fasted training rides in elite cyclists. He has found that by restricting intake before and during training rides, cellular levels of AMPK are increased in young and fit sports men. AMPK is a signalling mechanism for new mitochondrial growth, which can therefore be viewed very positively within this research enquiry. But, as I said, there are always two sides to every story: by restricting nutritional intake, the cyclists’ exercise capacity was severely diminished, plus p70S6K cellular activity was much lower than during fed scenarios. p70S6K supports muscular anabolic activity post-exercise - in other words, in a bodybuilder’s language, “you have to feed the machine!”

These research observations - that there are pros and cons around the use of IF - were made with young and fit cyclists. However, what happens when you step into my clinic room, where my average client is a burnt out, over-enthusiastic amateur athlete? In my clinical experience, the overtraining syndrome (OTS) discussed in sports medicine circles and the adrenal fatigue/exhaustion discussed in nutritional therapy and functional medicine, are pretty much one and the same. In both cases, there is not a neat collection of symptoms that can be easily diagnosed and named, but there is always some degree of health and performance decrement in that athlete. In these cases, if we consider the diminished ability of the adrenal glands to produce cortisol (our main stress hormone), our priority is therefore to support the athlete’s adrenal glands, so that they can gradually return to their previous energetic levels.

From a nutritional perspective, we support adrenal function by eating in a way to balance blood sugar levels. During periods of time when we are not eating, our blood sugar levels would tend to drop towards hypoglycaemia if it were not for the production of cortisol from our adrenals. Cortisol has an important role in gluconeogenesis, by which glucose is produced from fat and protein for blood sugar support; this is especially important during exercise activity. So, by imposing an IF regime on an athlete who is overtrained, their adrenals are likely to become weaker due to the additional demands placed upon them. If they include a training session within that fasted period, the toll is substantially higher on their poor adrenals. Additionally, the elevated levels of cortisol that are associated with moderate- to high-intensity exercise (especially in a glycogen depleted state), stimulates the breakdown of muscle tissue - hence, the athlete is in a catabolic state, not a supportive anabolic recovery state post-exercise.

In summary, I’ve tried to give you a view of the ‘other side of the story’; a taster of the physiological stress imparted by following an IF regime, especially in an adrenally fatigued individual or overtrained athlete. I’ve modelled my discussion around the adrenal glands, but further discussion could include the thyroid and pituitary glands, sex hormone balance, mitochondrial function, and inflammatory/oxidative stress status. Ironically, some of the purported benefits of IF can also display as a negative physiological drawback when fasting is implemented during a metabolically stressful period of time, such as exercise. We also need to recognise the genetic uniqueness of athletes, and note that IF will suit some individuals better than others. Nutrigenomics testing is not sensitive enough to pick up these subtleties yet, but the experienced eye of a sports nutrition specialist who considers health as an important entity should be able to pick it up. 

As practitioners working with athletes, whether elite or recreational, it is our jobs to consider both sides of any scientific or media headline, and to use our best clinical judgement regarding what we recommend to our athletes. This advice won’t be static either - IF might not be suitable for a particular athlete on hard training days, but on a peaceful, non-stimulatory day, it might work perfectly… As the phrase says, used ‘intermittently’ it may be a great tool, but we need to question the daily pattern - often it is just a good excuse to skip breakfast!