Intermittent fasting is the voluntary abstinence from food for a prolonged period of time.
Traditionally many cultures and religions have used fasting in
Some Christians follow lent. The Muslim religion has Ramadan where fasting
is observed for 29-30 days during the daylight hours.
Buddhist monks and nuns following Vinaya rules commonly do not eat
each day after the noon meal, aiding in meditation and good health.
Intermittent fasting is an umbrella term for various eating diet
plans that cycle between a period of fasting and non-fasting over a defined
period. Intermittent fasting is under preliminary research to assess if it can
produce weight loss comparable to long-term calorie restriction.
Many believe that fasting is the most ancient secret to good
There have been many studies on various intermittent fasting diets
that show that intermittent fasting can improve health and successfully aid in
For the purpose of this paper I would like to further explore:
- Periodic fasting (where, once every few months
you cut your food intake down for 5 days in a row)
- The 5:2 approach (where you restrict your
calories for 2 days a week)
- Time Restricted Eating (where you restrict
your eating to a narrow time window)
Professor Valter Longo, one of the leading experts on human ageing
believes in the power of fasting to delay aging. Periodic Fasting claims to
activate a process called autophagy which means ‘self eat’. Autophagy acts to
eat up dead, diseased, worn out cells. It is triggered by fasting and stops
when the fast is broken (https://valterlongo.com/ VAlter Longo Foundation).
Periodic fasting also claims to regenerate cells faster. So, when
you fast your system tries to save energy and recycles a lot of the immune
cells that are not needed. When the fast is broken it triggers the creation of
new more active white blood cells. (Valter Longo).
Short periods of fasting have been shown to regenerate the immune
system (Longo, Valter et al 2014)
A 2012 Human trial conducted by Valter Longo of a 4 day fast
resulted in IGF1 levels decrease (Insulin like Growth Factor -1) which is a
measure of cancer risk. Valter concluded
that regular bouts of short term fasting can reduce your risk of a variety of
cancers. And, that fasting could assist with making chemotherapy more effective
by slowing down the growth of cells to help protect the healthy cells during
He also recognised the difficulty of fasting for patients while
undertaking chemo therapy and there are current trials on an 800 calorie diet
to try to mimic this approach.
The general idea behind the 5:2 diet is calorie restriction on
the two (non-consecutive) given days. That is, for two of the 7 days in each
week, you eat very low calorie (but high in nutrition) foods, while the other 5
days you can eat what you would usually eat. This diet isn’t a full fast, but
is a carefully planned eating plan for a couple of days each week.
The two days of fasting requires you to keep your intake below a
set number of calories: 500 for women, 600 for men. The normal average calorie
intake is 2000.
5:2 Raised blood sugar and heart health
The diet has shown to reduce the HbA1C levels. This haemoglobin is
chemically linked to glucose. The formation of the sugar and haemoglobin
linkage indicates the presence of excessive sugar in the bloodstream, often
indicative of diabetes. A1C is of particular interest as it is easy to detect.
A human study concluded that intermittent fasting can reverse Type
2 Diabetes (Therapeutic use of Intermittent fasting for people with Type 2
diabetes as an Alternative to Insulin https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6194375/)
The study was of 3 patients all on medication to manage their
diabetes. The most noteworthy
outcome from this case series is the complete discontinuation of insulin in all
It was noted that caloric restriction
and weight loss are important factors for remission of T2 diabetes.
The study concludes that therapeutic fasting can provide superior
blood glucose reduction compared with standard pharmacological agents.
A 2018 study shows that modest weight loss of 5-10% have been
associated with significant improvements in cardiovascular disease risk factors
(eg decreased HbA1C levels. Reduced blood pressure, increase in HDL
cholesterol, decreased plasma triglycerides) in patients with T2 diabetes. The
risk factor was reduced even more with a greater body weight percentage weight
loss of 10-15% (Antoni R, Johnston KL et al. Intermittent v. Continuous energy
restriction: differential effects on postprandial glucose and lipid metabolism
following matched weight loss in overweight/obese participants. Br J Nutr.,
The 5:2 has also been found to have promising results for Brain
disease and Breast cancer
Time restricted eating is not a new diet but rather an ancient
ritual that has been observed by both religious and cultural groups.
The two most popular fasting schedules which have become popular
amongst body builders and celebrities is the 12:12 fasting:eating or the 16:8
fasting:eating. There have been some studies indicating that the 16:8 is the
According to Dr Satchin Panda, Professor at the Salk Institute in
San Diego, one of the worlds leading research centres for biomedicine in San
Diego, most of your body’s fat burning occurs 6-8hours after your last meal.
A human trial of TRE found that after 10 weeks, a group that had
gone without food for an additional 3 hours per day had lost more body fat, and
had bigger falls in blood sugar levels and cholesterol.
A recent clinical trial with 43 participants conducted comparing
Continuing Energy Restriction (CER) and Intermittent Energy Restriction (IER) concluded
that reductions in body weight were similar.
Fasting plasma glucose concentrations decreased after CER but not after
IER (mean difference CER–IER – 4.8% (0.7, 8.9), P < 0.05)
and fasting plasma non-esterified fatty acid concentrations were lower after
IER compared to CER (mean difference CER–IER 0.15 mmol/L (0.06, 0.24), P < 0.005).
There were no differences in lipids, adipokine/inflammatory markers, ABP or HRV
between diets (Pinto et al)
They concluded that short-term CER
or IER diets are comparable in their effects on most markers of cardiometabolic
risk, although adaptive changes in glucose and fatty acid metabolism occur.
A major assumption that intermittent fasting makes is that the
food that is being consumed on the non-fasting days along with the restricted
or fasting days will still equal a calorie deficit. Eating healthy on non fasting
days does not mean that a calorie deficit will be maintained as eating
‘healthy” can mean a lot of different things to many people.
Another consideration is that on the fasting days or low calorie
days are foods from different groups being consumed. If a patient is eating the
same foods over and over again there could be risk of nutrient deficiencies.
There is more quality research coming through on intermittent
fasting and more human trials that I could cover in this paper.
Many books on how to fast and recipe books for fasting diets have
been published creating a small market of products.
If a patients chooses to go on this diet they will need to ensure
that they are taking in quality healthy ingredients such as fruits, vegetables,
wholegrains and lean protein.
There could be a risk associated with grains and fruit being
omitted from the diet as these are generally higher in calories.
In conclusion, a wholefoods diet would be favourable over intermittent fasting in the first instance. If a patient is unable to lose weight on a wholefoods diet then calorie restriction or one of the fasting techniques outlined here could assist in restricting calories. Intermittent fasting could add value as a tool to assist calorie restriction and weight loss if other more gentle approaches have not been successful. Intermittent fasting isn’t a ‘magic’ remedy for reversing diabetes or heart health but a valuable tool to help patients lose weight if they haven’t been able to previously.
- https://valterlongo.com/ Valter Longo Foundation/PKA to promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression. Cell Stem Cell, 2014; 14(6)
- Valter D. Longo et al. Prolonged Fasting Reduces IGF-1
- Therapeutic use of Intermittent fasting for people with Type 2 diabetes as an alternative to Insulin https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6194375/
- Antoni R, Johnston KL et al. Intermittent v. Continuous energy restriction: differential effects on postprandial glucose and lipid metabolism following matched weight loss in overweight/obese participants. Br J Nutr., 2018. http://www.ncbi.nlm.nih.gov/pubmed/29508693
- Pinto et al (2019) Intermittent Energy Restriction is comparable to Continuous Energy Restriction for Cardiometabolic Health in Adults with central obesity; A randomised controlled trial.