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Intermittent Fasting


Intermittent Fasting

Please no more diets! You have tried them all and over the past 15 years, the advice from friends, the internet, best-selling books, has changed considerably. I would bet though, that one such diet, has worked, and is still working for someone you know. Of course, I am referring to intermittent fasting (IF). I’m  Gareth Nicholas, head nutritionist at Maximuscle and let me share with you my thoughts and the current scientific understand of IF. How and why it works and how you could implement and try such a diet.

Where did it all start?

The birth of IF was in trying to help those individuals that were morbidly obese. People that without taking drastic measures would ultimately die and early death. Fortunately, results from following an IF diet were profound, in part due to immediate effects on weight loss and the reduction in the psychological barrier to losing weight in this population of people. Thankfully, not everyone falls into the morbidly obese category, but some form of IF may still be helpful in maintaining or losing weight or indeed to improving general health and well-being.

Intermittent fasting Paleo Hunter Gatherer

Dietary Evolution

Of course things change, the world evolves, we evolve, albeit very slowly, but it's interesting that as mammals we have been built to withstand periods of food scarcity. The liver and adipose tissue act as a larder in times of starvation by storing energy for later use. There is however a societal conflict - in this day and age societies and communities no longer need a self-storage, as food is just around the corner – the day of the hunter gatherer is a thing of the past. In spite of this, a growing dietary trend, particularly in overweight individuals, is fasting. Fasting has been a religious practice for centuries but dietary fasting for weight loss is a more recent phenomenon. This article is going to concentrate on the three most observed and researched dietary fasting practices:

  • ADF - Alternate Day Fasting (70% energy restriction every other day).
  • IF - Intermittent Fasting (16-48h) (500-700 kcal a day for 2 consecutive days per week).
  • TRF - Time Restricted Feeding (8h or less) (restricted for intake to a particular time.

Olympian Lauren Williams on making weightElite trainer and coach Chris Rigby

Fasting - which one is best and why?

Let me explain it like this. If you have a small fridge (fat storage) you'll need to go to the shops more often and less likely to cope with long periods of minimal food (fasting). In context, this is what is likely to be observed within non-obese individuals. Whereas if you have a medium to large fridge (overweight to obese) your shopping requirement and the tolerance to fasting will be much greater compared to the non-obese. As such longer fasts, such as IF and ADF are better dietary regimes for obese individuals and TRF would possible work better for non-obese individuals.

The benefits of fasting can stretch to a wider audience than just the morbidly obese, but the fasting period needs to be tailored to the individual. Fasting can be difficult especially in the early days of a diet but why do it at all?

CrossFit coach and athlete Daine Mitchell

Benefits of fasting

Less in more out, the mathematics of weight-loss seems very simply, however the practical application is likely to be more difficult, but clearly fasting is an obvious suggestion to help instigate weight loss. Putting that aside for a minute, fasting also appears to offer a multitude of health benefits:

  • Enhanced cognitive function especially in older individuals,
  • Increased insulin sensitivity,
  • Ketone generation & activation, lipid (fat) mobilisation,
  • Decreased resting heart rate and blood pressure,
  • Reduction in body and visceral fat,
  • Improve longevity.

What does the science say?

From the scientific data it is clear to see that despite an individual’s first thought of fasting, it actually has a high percentage of completion compliance, compared to more conventional caloric restricted diets (CRD). It also has a high percentage of helping people change/improve their eating habits in the non-fasting days. On face value, it all looks promising but it must be noted that there are very few randomised controlled trails (RCTs) that have assessed fasting diets versus CRDs. The few studies that have compared the two regimes over a relatively short period of time have still identified the potential of intermittent fasting. As mentioned early in this article, most of the studies conducted in fasting have been in the morbidly obese population and therefore potentially limits any generalisation. The last and possibly most important point before locking up your cupboards is the fact that to date no long term studies have been completed, so there is little to no data to prove or disprove any long term effects of fasting.

Thinking about giving it a try?

One thing is for sure, this is definitely an interesting area of nutritional science and one that may have some significant benefits to reducing the every growing obese population. My advice would be give it a try, but to really try it, you need to plan it all out. What work or social engagements cause problems when fasting? Be prepared to feel more tired on fasting days, especially in the early weeks of following IF. Perhaps avoiding training on those days, to start with. Fasting doesn’t have to mean, completely nothing. I would still advise having approximately 500 calories on fasting days. Ensuring that you are consuming some micronutrients to boost immunity and health. I would also recommend consuming approximately 40-80g of protein on these days. Hopefully, that will help protect your existing muscle mass, as this is likely to be compromised when following such a calorie and carbohydrate restriction. Protein supplements, such as powders and bars, can be a convenient source of protein. Taking out the guesswork and providing alternatives with less carbohydrate and fat from typical food sources.

Always consult professional advice before changing your dietary habits.


Antoni, R., Johnston, K. L., Collins, A. L., & Robertson, M. D. (2017). Effects of intermittent fasting on glucose and lipid metabolism. Proceedings of the Nutrition Society, 1-8.

Dong, T. A., Sandesara, P. B., Dhindsa, D. S., Mehta, A., Arneson, L. C., Dollar, A. L., Taub, P. R., & Sperling, L. S. (2020). Intermittent Fasting: A Heart Healthy Dietary Pattern?. The American journal of medicine, 133(8), 901–907.

Matarese, L. E., & Pories, W. J. (2014). Adult Weight Loss Diets Metabolic Effects and Outcomes. Nutrition in Clinical Practice, 29(6), 759-767.

Mattson, M. P., Longo, V. D., & Harvie, M. (2016). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews.