X-PERT Blog: The many myths of intermittent fasting…
Matt Whitaker – Researcher and Trainer in Public Health
What is fasting?
Intermittent fasting (IF) is one of the dietary approaches presented throughout the X-PERT Programmes. IF is defined as a voluntary, preselected period of time where no or very few calories are consumed followed by an allocated time when the fast is broken. Usually this period of abstaining from calories lasts a matter of hours as opposed to days.
Intermittent fasting can be sub-categorised depending on the length of the fast and whether it is a true fast. The three most acknowledged and researched variations are:
1) 5:2. This type is not a true fast as it limits energy intake for two days a week as opposed to completely abstaining from all calories. The limits encouraged are: less than 500kcal/day for women and 600kcal/day for men and it is not advised to undertake the two ‘fasting’ days consecutively.
2) Time-restricted eating (TRE). This approach sees the individual select an eating window (such as 10am to 6pm) and completely fast for the remainder of the day. TRE can be performed every day or just certain days and if commonly performed by skipping breakfast and extending the overnight fast.
3) Alternate day fasting. This is an extended version of TRE where an individual will only have one meal each day and at the same time, demonstrating a full 24 hour fast in between meals.
Scepticism surrounds intermittent fasting, potentially as a result of the numerus myths circulated about the dietary approach. The majority of this negative persona is based on absolutely no research but instead through assumptions and misconceptions. This section aims to dissipate these myths, hopefully reducing barriers associated with IF.
Myth 1 – Fasting slows your metabolism
Metabolism reduces when one decreases body weight, this is inevitable but the damage can be limited. If an individual deprives themselves from both dietary perspectives and stored energy reserves their metabolism will reduce as a protective repercussion.
Depriving oneself from a dietary perspective is relatively associated with the amount of energy consumed and is inevitable if the goal is weight loss. However, any deficit in energy in can be counterbalanced if the body can readily access its stored energy (fat).
The body can readily access stored fat as an energy source when levels of the storage hormone, insulin are low. In principle, if one has low levels of insulin they will be better able to access their stored fat so there will not be a need for metabolism to reduce as the body’s energy requirements are attained. When one is fasting insulin is as low as it can be for that individual, meaning fasting may even be protective when considering reductions in metabolism.
Myth 2 – Fasting is just starving yourself
Fasting is a voluntary action to only avoid food for a pre-selected, controlled period of time. True starvation is where no food is available for an undetermined period of time, out of the control of the individual.
When one is fasting their levels of circulating insulin are reduced, meaning they are receiving a constant supply of energy from fat stores and are thus not ‘starving’ themselves.
Myth 3 – Fasting makes you breakdown muscle
It has been suggested that one would need to fast for five or more consecutive days before any significant amount of muscle is utilised for energy.
Muscle tissue is continuously broken down and rebuilt and fasting can encourage this process, through promoting autophagy i.e. the clearing of old proteins with the replacement of newer ones; less likely to get damaged – this is a good thing!
Studies on fasting when combined with resistance training have actually shown beneficial effects in strength and hypertrophy of worked muscles. This may be partly explained due to fasting increasing growth hormones.
Myth 4 – Fasting will deprive you of essential nutrients
Long-term clinical studies do not evidence malnutrition or nutrient deficiency in participants in the fasting groups.
Real emphasis should be put on the quality of foods when breaking the fast. Focusing on avoiding processed, nutrient-poor foods and increasing consumption of nutrient-dense, unprocessed foods will lead to the avoidance of nutritional deficiencies.
Lastly, there is potential for some stored, fat soluble vitamins to be released into circulation from fat stores when they are easily accessible.
Myth 5 – Fasting just makes you hungry all the time and skipping a meal leads to overcompensation at the next meal
Studies have shown that when one skips a meal they may eat slightly more at the next meal but not enough to compensate for the skipped meal. Imagine one eats 500kcals for breakfast and 500kcals at a buffet lunch; the next week they skip breakfast and are offered the same buffet lunch, where they eat 700kcals. In this case the individual has eaten more at lunch when they skipped breakfast, but still less overall.
Fasting has been shown to reduce hunger hormones that drive appetite and increase satiety hormones that promote fullness. Some may feel hungry at first but once established on an IF routine most report reduced hunger.
Myth 6 – Breakfast is the most important meal of the day
The thought behind this is that breakfast gives you the energy boost you need to start your day. In reality if one didn’t eat in the morning their body would compensate by increasing levels of adrenaline, growth hormone and cortisol which in-turn will release glucose from the liver; physiologically giving you the energy you need to start your day. Therefore consuming food upon waking is not essential.
Additionally the word breakfast is generally associated with eating upon waking. However, once the word is broken down (break-fast) it is more ‘socially acceptable’ to recognise it does not matter what time one breaks their overnight fast.
There are several types of fasting and there is evidence that supports their potential in overall health and weight management. Unfortunately these benefits are often overshadowed by myths advocated by assumptions that put many off even attempting IF.
Intermittent fasting is just one of the dietary approaches we advocate. If one is concerned that their current dietary approach is not allowing them to achieve their health goals they should not be put off trying IF by any of the dispelled myths discussed throughout this blog!
Any questions, feedback and/or suggestions would be most welcomed, as is any request for the research supporting this blog. Please email me at