Is Intermittent Fasting The Secret To Weight Loss?

Is breakfast still the most important meal of the day? We’re exploring the sense and nonsense surrounding intermittent fasting and calorie restriction for weight loss and longevity.

“Obese people and those desiring to lose weight should perform hard work before food. Meals should be taken after exertion and while still panting from fatigue. They should, moreover, only eat once per day and take no baths and sleep on a hard bed and walk naked as long as possible.”

Hippocrates recommended his patients to fast and exercise to achieve the best results.
Since then this advice has been tipped on its head, and we’re told that breakfast is the most important meal of the day and that skipping it could be the cause of additional weight gain.
So, where does the truth lie?
There is research indicating that people who skip breakfast tend to have an unhealthier weight than people who do eat breakfast. However, often this research is looking at correlation rather than causation. Breakfast skippers have also been found to have the lowest quality diet and therefore it’s hard to say whether breakfast skippers are more often overweight because they skip breakfast or due to their poor diet choices.
Recently, the advice from Hippocrates surrounding fasting, has gained popularity once again. It is now thought that skipping breakfast and postponing the first meal of the day until lunchtime, say around 12/1pm could actually be beneficial. This is according to Martin Berkhan’s “lean gains” protocol, a popular strategy for weight-loss, also claiming to help you live until you’re 100.
But how much of said claims really have any links to reality and are supported by science backed evidence.
Does intermittent fasting have to be calorie restrictive?

Fasting is the simple concept of not eating and we do it all the time during our sleep. Some religions require their followers to fast at some point during the year as part of religious protocols. Intermittent Fasting (IF) simply means you’re not eating for a long period of time followed by shorter time frames of normal eating. There are several strategies to do this. For example, you can either fast every day and restrict your eating window to 8-10 hours or fast an entire day every 2 days, with no food passing your lips!
IF is not the same as calorie restriction (CR). You can still fast without restricting calories. To do this, you simply eat the same number of calories within a shorter time frame. In this case you will not lose weight. You can even gain weight whilst fasting if this is your goal. As long as you are eating in a calorie surplus in the time frame you’re allowed to eat, you’ll be adhering to the energy balance equation. When it comes to losing, or gaining weight the energy balance still determines the outcome. Research that compared 2 groups eating the same amount of calories either in 24 hrs or in a time-restricted window, consistently found no difference between groups.
Having said that, IF can be used as a tool to help create a calorie deficit, because in many cases simply restricting the time window in which you can eat, naturally leads to a reduction in overall calorie intake. So Intermittent Fasting combined with Calorie Restriction can be an effective method to lose weight. However, there is a risk of overeating in the timeframe you are allowed to eat so if your goal is weight loss, keeping track of your calories is essential. That is, if you’re not on this super handy healthy meal prep service called FFF of course. Conclusion, IF alone, does not cause weight loss.
Fasting to live forever

We are living in an unusual time where most of us have never known famine. During the majority of human history this was quite common and therefore we have adjusted to cope with starvation well. Fasting is nothing but voluntary starvation. The longest recorded fast completed was 382 days and was carried out by a heavily obese 27 year old man who started at a weight of 207 kg. During his fast he was allowed water and they also gave him vitamin supplements to prevent micronutrient deficiencies, as well as ensuring he was closely monitored by a full medical team. In short he basically didn’t eat for over a year. Can you imagine that? Under supervision of doctors he reached a healthy weight of 80.6 kg and amazingly managed to keep it off, maintaining a healthy weight even five years later. Even though this is an extreme case study and the subject was incredibly obese, it shows our bodies can tolerate more than you might think. We seem to be better adjusted to deal with too little than with too much food. It is hypothesised that fasting might activate a survival mechanism and that is what could prolong lives.
When we eat, our bodies spend a significant period of time digesting a meal and absorbing the nutrients. Our blood glucose levels and as a result insulin levels go up to transport the glucose and other nutrients into our cells. Any excess that isn’t used instantly will be stored as fat or glycogen. Depending on the size of the meal and the energy expenditure of the person, these concentrations will gradually go down and after 8-12 hours we are no longer digesting a meal. This is called the fasted state and supposedly where the magic happens.
What happens if we don’t eat?

In the fasted state our bodies will rely on their fat stores to support the ongoing need for energy, therefore you’d be burning fat. If there’s no food to be digested, glucose and insulin in your blood will be low. Low insulin levels will cause an increase in the production of stress hormones. Since there is no glucose to be taken up, glucose will be synthesised from protein (muscle and other tissues) and converted from stored glycogen under the influence of the hormone glucagon. Growth hormone production and metabolic rate will be reduced, this effectively means your body anticipates the lack of food and becomes conservative with energy. Many of these effects are also consequences of calorie restriction.
Research in animals has shown that calorie restriction extends their life. Digesting food is a form of stress on the body and even though this is normal, it creates free radicals in the process: reactive particles that can damage body tissues if they build up too much. Fasting reduces the production of free radicals and combined with the reduced metabolic rate this may prolong life. Fasting is found to have positive effects on disease prevention of diabetes, cardiovascular disease, some cancers and strokes, but also neurological diseases. The idea is that if our bodies don’t need to deal with the stress of digestion it allows for it to focus on repairs. However, most of this research is done on animals and the exact mechanisms are unknown.
The sweet spot

Most of the research done on the effects of fasting and calorie restriction on health is done with animals. Therefore, results can’t be translated directly to humans. However, a recent trial done on non-obese humans found very similar effects when they put subjects on a calorie restricted diet. Over 2 years they lost weight and their metabolism slowed down beyond the point of which could be expected based on the weight loss alone. They also found that oxidative stress (production of free radicals) was reduced. Whether this effectively extended their life is unclear. Important to note is that there is a sweet spot here, the participants were put on a calorie deficit of only 15%. Going without food for too long can have negative health effects, mentally as well as physically.
One of the consequences of fasting is a reduced rate of protein synthesis (needed for muscle growth), and an increased rate of glucose production from protein. Aside from fat, our bodies also tend to breakdown muscle tissue for energy supply. Therefore, negative effects on muscle growth and maintenance can be expected. However, this doesn’t mean you’ll instantly lose all your gains if you do give IF a try.
There’s little evidence surrounding fasting on humans and even less on trained subjects. A trial done with 34 resistance trained males found no adverse effects of a 16 hour intermittent fasting regime compared to a regular diet on muscle size or strength. Amazingly, even though the subjects were not on a calorie deficit the Intermittent fasting group lost more fat than the control group so IF could therefore be useful for body recomposition. The effect was small and this is only one study, therefore more research is needed but it is a promising prospect.
The bottom line

Fasting without calorie restriction does not cause weight loss. Intermittent fasting can be used as a tool to create a calorie deficit and therefore can lead to weight loss. Health benefits of IF seem to come mostly from calorie restriction, not necessarily the fasting in itself. Even though calorie restriction extends the lifespan of animals, it is unclear if this mechanism works the same way in humans, but new research indicates it might.
Fasting is essentially a systematic way of starving yourself, in which muscle will be broken down at some point. It is important to find the sweet spot as fasting for too long and creating a calorie deficit that is too large will have adverse effects. So yes, IF can help you lose weight if combined with a calorie deficit and this may improve your health and extend your life. As you do not need to fast to restrict calories, it is also possible that the same results can be achieved without fasting.


  1. Betts, J.A., Richardson, J.D., Chowdhury, E.A., Holman, G.D., Tsintzas, K. and Thompson, D. (2014). The causal role of breakfast in energy balance and health: a randomised controlled trial in lean adults. The American Journal of Clinical Nutrition, 100 (2), 539-547.
  2. Horne, B.D., Muhlestein, J.B. and Anderson, J.L. (2015). Health effects of intermittent fasting: hormesis or harm? A systematic review. The American Journal of Clinical Nutrition, 102 (2) 464–470.
  3. Leech, R.M., Worsley, A., Timperio, A. and McNaughton, S.A. (2015). Understanding meal patterns: definitions, methodology and impact on nutrient intake and diet quality. Nutrition Research Reviews, 28, 1–21.
  4. Mattson, M.P., Longo, V.D. and Harvie, M. (2016). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews.
  5. Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q.F., Battaglia, G., Palma, A., Gentil, P., Neri, M. and Paoli, A. (2016). Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body compostion, inflammation and cardiovascular risk factors in resistance-trained men. Journal of translational Medicine, 14(290).
  6. Redman, L.M, Smith, S.R., Burton, J.H. Martin, C.K., Il’yasova, D. and Ravussin, E. (2018). Metabolic slowing and reduced oxidative damage with sustained caloric restriction support the rate of living and oxidative damage theories of aging. Cell Metabolism 27(4) 805-815.
  7. Stewart, W.K. & Fleming, L.W. (1973) Features of a successful therapeutic fast of 382 days’ duration. Postgraduate Medical Journal (March 1973) 49, 203-209
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