Intermittent Fasting
What’s all the hype about?
What is it?
Intermittent fasting (IF) is less of a diet and more of an eating pattern that suggests when to eat, rather than what to eat.
How do you do it?
There are a few different types of IF, including:
1. Alternate day fasting: involves fasting days where no food or calorie containing beverages are consumed, alternating with days where food is consumed ad libitum (as desired).
2. The 5:2 diet: involves severe energy restriction on two non-consecutive days a week and ad libitum eating on the other five days.
3. Time restricted eating: involves ad libitum food intake within a specific window (usually 7-10 hours per day eg. 9.30am-6.30pm), which induces fasting periods on a daily basis.
From an evolutionary standpoint periods of fasting make more sense than eating three meals a day at set times, given ancient hunter gatherers didn’t have supermarkets, refrigerators or food always readily available. They often went long periods without food which has created adaptive responses in humans to be able to continue functioning while in a fasted state.
Are there any benefits?
The vast majority of IF research has been conducted in animals, and evidence in humans of health improvements is preliminary, therefore further research is required to confirm the below.
BUT there is evidence to suggest not only can it help people who are trying to lose weight by reducing overall calorie intake and utilising fat stores for energy, there seem to be other metabolic effects that may lead to health benefits for the wider population.
What’s the science?
When we eat, food is broken down into glucose, but usually more is ingested than we can immediately use, therefore some must be stored away for later. Insulin is released in response to glucose and helps store the excess in the liver (glucose is linked together in long chains to make glycogen, the storage form of glucose). The liver however has limited storage space for glycogen so excess is turned into fat of which some is stored in the liver but most is stored in fat deposits in the body (where there is no limit to the amount that can be stored!).
During fasting, insulin levels reduce which results in stored energy being used. Firstly glycogen stores are depleted, which creates a metabolic shift to mobilise fat stores and generate ketones for energy use. Therefore as well as weight loss there may be a reduction in fat mass while fat free mass (including muscle) is preserved (adequate protein intake and exercise are important in the potential success of this).
IF creates lower blood glucose and lower insulin levels which increases insulin sensitivity, and therefore perhaps reduces the risk of diabetes and heart disease. A lower risk of heart disease is also suggested through the beneficial reductions in cholesterol and triglycerides. Lower insulin levels also increase human growth hormone which plays a key role in growth, increasing muscle mass and bone density, cell repair and metabolism.
Fasting also triggers a short term stress response which may create a long term enhanced ability to cope with more severe stress and therefore potentially counteract disease processes. Some studies suggest fasting can reduce inflammation which is an important risk factor for some chronic diseases, and assist with cancer prevention through protecting cells from DNA damage, suppressing cell growth and enhancing apoptosis (planned death) of damaged cells.
Fasting regimens also appear to have some positive impacts on the gut microbiota, as well as increased alertness and mental acuity, and there may also be links to reduced cognitive decline with ageing and risk of Alzheimer’s disease.
Bottom line
The most important thing about choosing what and when to eat is choosing something that you can stick to, and avoiding yo-yo dieting between fads where weight is lost and regained and overall health is not optimised. Remember IF isn’t the magic fix, so it’s important that when you do eat you make healthy choices to ensure your body gets the nutrition it needs. The goal is consistent healthy habits.
Takeaway message
Limit the eating window in the day to 7-10 hours, minimise snacking, stay hydrated, get adequate sleep, and when you do eat try most of the time to – eat real food, not too much, mostly plants.
References
https://www.sciencedirect.com/science/article/pii/S1550413118302535
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3946160/
https://academic.oup.com/ajcn/article/102/2/464/4564588
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5411330/
https://www.ncbi.nlm.nih.gov/pubmed/23171320