Intermittent fasting: what you need to know before starting
The primary intent with a fast is often weight loss, but science has revealed that regular periods of fasting can provide physiological benefits such as reduced inflammation, increased autophagy (“cellular cleansing” ), resistance to stress or the rebalancing of the intestinal microbiota .
Our body has evolved and adapted to be able to go without food for several hours or even days. In prehistoric times, before agriculture, hunters and gatherers evolved to survive - and thrive - for long periods without eating.
Nowadays, this rhythm has changed, we are more and more sedentary, staying awake for long hours in front of computers, TV, on our phones, with blue lights that disrupt our natural circadian rhythm. We have enough to eat at any time of the day and often our pace of life and stress lead to snacking and late dinners.
It is these extra calories, less physical activity and ubiquitous stress that are the causes of obesity, type 2 diabetes, cardiovascular disease or other diseases of civilization. But scientific studies show that intermittent fasting can help reverse these trends.
What is Intermittent Fasting?
Intermittent fasting is the voluntary avoidance of food and drink (except water) within a chosen amount of time, for health, wellness, spiritual or religious reasons.
What happens physiologically?
When we eat, we take in energy in the essential form of glucose and fatty acids, which we can use immediately, or store for later.
Insulin is the key hormone involved in the storage of food energy. It helps to store excess energy in 2 distinct ways:
- Glucose (sugar) is stored as glycogen in the liver or muscles. However, the glycogen storage space is very limited and, once this space is reached, the liver begins to convert excess glucose into fat, in the fat cells ( unlimited storage! ).
- The process is reversed when we do not eat; insulin levels drop, which tells the body to start burning stored energy. Blood sugar drops, and the body must then draw glucose from the reserves. Glycogen is the most easily accessible source of energy, and can provide enough energy to meet the body's needs for 24 to 36 hours. Then the body will break down fats for energy.
The benefits of intermittent fasting
When fasting is combined with a healthy diet and lifestyle, it can bring some interesting benefits:
- Feeling of satiety
- More energy
- Decreased insulin and blood sugar levels
- Improved mental clarity and focus
- Stimulation of autophagy ("cellular cleansing")
- Possible reduction of low-grade inflammation
On the other hand, it is not because the fast is long that it is necessarily better. Sometimes the body needs more flexibility to get better results. This is where considering individuality is important, it's all about balance.
Which intermittent fasting to choose?
There are several approaches and ways to practice intermittent fasting:
- If you have never fasted, it is good to start with the TRE: leave 12 hours between dinner and breakfast, only hydrate with water.
- For the 16:8 fast : we finish dinner at 8 p.m., we do not ingest anything, except water, until noon the next day (some fasts “accept” coffee, tea or herbal tea without sugar).
- The 5:2 method involves eating regularly 5 days a week. The other 2 days are limited to a 500-600 calorie meal.
- For OMAD , we limit ourselves to one meal a day.
The idea is not necessarily to reduce calories but to bring them to specific windows and leave your body in digestive rest , which allows it to "take care" of other functions that need attention.
It's up to you to choose the one that suits you best, listen to your needs . There are people who prefer to fast in the morning, and others in the evening, more or less long. It is possible to do it once a week or several times, or by periods. This can be a good regulating strategy after a hearty dinner or a festive weekend.
Fasting puts the body under stress, hormetic stress . This moderate stress is usually a good thing – pushing the body into autophagy, which is the main appeal of fasting.
But when you're already too stressed from your daily life, you risk increasing your stress level even more. This increased secretion of cortisol can have the opposite effect of what is sought with fasting: for protection, it risks gaining fat mass in favor of muscle mass. If there is chronic fatigue, do not force your body.
What to eat before and after a fast?
Now is not the time to jump on a burger or a pizza. Instead, focus on nutrient-rich foods to support fasting and live it better. Fiber-rich, unprocessed, whole foods that offer variety and flavor.
The rainbow of vegetables and fruits, especially cruciferous vegetables, legumes, quality proteins such as fish or eggs, good fats; avocado, oilseeds, rapeseed oil, olive, virgin and cold-pressed flax. Nutrients that keep you feeling full.
A few precautions
Therapeutic fasts beyond 72 hours must be supervised by a health professional or doctor. Fasting is not recommended for children and adolescents, pregnant or breastfeeding women, people with diabetes or blood sugar problems, people with a history of eating disorders.
Intermittent fasting, if accompanied by a healthy diet and lifestyle, is an excellent tool for keeping your weight in balance or even losing weight, promoting the body's detoxification functions, regulating appetite and blood sugar which brings energy gain and mental clarity!
Lizette Scialom is a well-being and nutrition coach, certified "Mind Body Nutrition Coach". She practices at Center Vitruvius , a medical center specializing in comprehensive and integrative care of body and mind.
The Influence of Meal Frequency and Timing on Health in Humans: The Role of Fasting, Antonio Paoli, Grant Tinsley
Effects of Intermittent Fasting on Health, Aging, and Disease List of authors. Rafael de Cabo, Ph.D., and Mark P. Mattson, Ph.D.
Watch the Clock, Not the Scale, Kelli L. Vaughan
Early Time-Restricted Feeding Improves Insulin Sensitivity, Sutton et al., 2018, Cell Metabolism 27, 1212–1221
Diet and Feeding Pattern Affect the Diurnal Dynamics of the Gut Microbiome, Amir Zarrinpar. Cell Metabolism 20, 1006–1017
Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan, Valter D. Longo. Cell Metabolism 23, June 14, 2016
Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation but Does Not Affect Energy Expenditure in Humans, Eric Ravussin, Ph.D. 2019 August; 27(8): 1244–1254