Is Intermittent Fasting For You?

Intermittent Energy Restriction

Intermittent fasting has been gaining a lot of interest in the past few years, especially in light of the long-term ineffectiveness of Continuous Energy Restriction diets on the treatment of obesity.  (1) But what is it and how does it compare to Continuous Energy Restriction as a tool for weight loss? Here we review the latest scientific research and evidence for you.

Intermittent Energy Restriction involves “restricting energy intake to certain periods of the day or prolonging the fasting interval between meals” (1). Two forms of Intermittent Energy Restriction include:

  1. Intermittent Fasting (IF): where there is 60% energy restriction on 2–3 days a week, or on alternate days (1)
  2. Time Restricted Feeding (TRF): limiting the daily period of food intake to 8–10 hours or less on most days of the week (1)

The supposition of this approach is that individuals do not fully compensate during feeding periods for the energy deficit produced during the extended periods of fasting between eating periods. It is also presumed Intermittent Energy Restriction may be easier to follow and maintain over time than Continuous Energy Restriction. The final assumption is that Intermittent Energy Restriction may lead to metabolic adaptations that favour a greater loss of fat mass, the preservation of lean mass, and a greater ability to sustain weight loss (5).

Scientific Research for Intermittent Fasting and Weight Loss

But as with all new diets it’s important to move beyond assumptions and look at what the scientific research is saying – to understand the real benefits and potential risks.

So how does this form of weight loss compare to the traditional Continuous Energy Restriction diet for weight loss, which we have been experimenting with so far with in this course?  A review of 11 randomised trials lasting for more than 8 weeks with the focus on the outcome of “weight loss” found that Intermittent Energy Reduction is as effective in terms of weight loss as Continuous Energy Restriction. With 9 out of 11 trials showing no difference in weight or body fat loss. (1)

Promising effects on fat mass and insulin sensitivity have also been reported when fasting duration is routinely extended beyond sixteen consecutive hours (2), which is positive for improved body composition as well as reaching and maintaining a healthy weight.  These benefits are also found in Continuous Energy Restriction models. (7)

The challenge with these trials is that there are lots of exceptions to the rules so the time restriction can be inconsistent.  Further research will require the models to be tested with tighter controls to isolate whether any possible health effects of Intermittent Fasting are related to regularly extending time between meals, or simply to the net negative energy balance that comes from any form of dietary restriction. (2)

One shortfall of these studies is that they were conducted over a short period of time.  Further research is required to assess the ability to maintain the lost weight without regaining it and the long-term effects of such dietary changes. (3)

Some animal models have found that Intermittent Energy Restriction “reduces oxidative stress, improves cognition and delays aging.” (5) Additionally, Intermittent Fasting has been found to have anti-inflammatory effects, promotes the body’s ability to clear out old cells, and benefits the gut microbiome. The benefit-to-harm ratio varies by model, Intermittent Energy Restriction protocol, age at initiation, and duration. (5)

So far then, the research is showing that Intermittent Energy Restriction is at least as effective as Continuous Energy Restriction for weight loss and reduction in body fat.  Any other claimed benefits of Intermittent Energy Restriction need further trials to compare whether these benefits can also be achieved with Continuous Energy Restriction – so we can understand if it is the overall energy reduction or the prolonged periods between eating that are providing the benefits.

Is intermittent fasting for you?

Intermittent fasting is not a good strategy for everyone as it raises cortisol levels.  We have learned when blood sugar levels drop too low, if we do not eat something the body will release our stress hormone cortisol to raise blood sugar levels again. So for someone with challenges with blood sugar regulation or adrenal dysfunction, fasting would not be a good option. (4)

Intermittent fasting should also be avoided in times of increased stress. (6)

It probably goes without saying that Intermittent Fasting should also be avoided during pregnancy or breast feeding. (6)

Interested in trying Intermittent Energy Restriction?

One simple way to start to experiment with Intermittent Energy Restriction would be to extend the fasting period between your last evening meal (including an evening snack) and breakfast.  Try starting with 12 hours (eg last evening meal at 19.00 and breakfast at 07.00).  Remember if you are experiencing increased stress or challenges with your blood sugar control this approach may not be appropriate for you.

If you would like to explore more intense Intermittent Energy Restriction protocols book a call with our Nutritional Therapist so we can help you assess if this is the right tool for you.


  1. Corey A. Rynders et al, “Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss”. 2019 Link:
  2. 2020: Templeman I et al, “The role of intermittent fasting and meal timing in weight management and metabolic health”. 2020 Link:
  3. Ganesan A. et al, “Intermittent Fasting: The Choice for a Healthier Lifestyle”. 2018 Link:
  5. Mattson M.P., et al. “Impact of intermittent fasting on health and disease processes”. 2016 Link:
  7. Stockman M.C. et al, “Intermittent Fasting: Is the Wait Worth the Weight?” 2019 Link:

Comments are closed here.