There are numerous myths and facts floating around, in regards to intermittent fasting. Let's dive into this topic and provide a guide with the most common myths, I have come across.
1) Not eating breakfast makes you fat
Interestingly, this matter was recently settled in a randomized controlled trial, which is the gold standard of science.
This study was published in 2014 and compared eating breakfast vs skipping breakfast in 283 overweight and obese adults (https://www.ncbi.nlm.nih.gov/pubmed/24898236).
After a 16-week study period, there was no difference in weight between groups.
This study shows that it doesn't make any difference for weight loss whether you eat or don't eat breakfast, although there may be some individual variability.
There is no evidence that eating in the morning aids weight loss.
2) Eating frequently increases Metabolism
It is true that the body expends a certain amount of energy digesting and assimilating the nutrients in a meal.
This is termed the thermic effect of food (TEF), and amounts to about 20-30% of calories for protein, 5-10% for carbs and 0-3% for fat calories (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC524030/).
On average, the thermic effect of food is somewhere around 10% of the total calorie intake.
However, what matters here is the total amount of calories consumed, not how many meals you eat.
Eating six 500-calorie meals has the exact same effect as eating three 1000-calorie meals. Given an average thermic effect of 10%, it is 300 calories in both cases.
This is supported by numerous feeding studies in humans, showing that increasing or decreasing meal frequency has on total calories burned (https://www.ncbi.nlm.nih.gov/pubmed/9155494).
3) Smaller more frequent meals help reduce weight
Frequent meals do not boost metabolism (increase calories out).They also do not seem to reduce hunger (reduce calories in).
If eating more frequently has no effect on the energy balance equation, then it shouldn't have any effect on weight loss.
In fact, this is supported by science. Most studies on this do show that meal frequency has no effect on weight loss (11Trusted Source, 12Trusted Source).
For example, a study in 16 obese men and women did not find any difference in weight, fat loss or appetite when comparing 3 and 6 meals per day (13Trusted Source).
However, if you find that eating more often makes it easier for you to eat fewer calories and less junk food, then perhaps this is effective for you.
4) Your Brain Needs a Constant supply of Glucose
Some people believe that if we don't eat every few hours, that our brains will stop functioning.
This is based on the belief that the brain can only use glucose (blood sugar) for fuel.
However, what is often left out of the discussion is that the body can easily produce the glucose it needs via a process called gluconeogenesis (14Trusted Source).
This may not even be needed in most cases, because your body has stored glycogen (glucose) in the liver that it can use to supply the brain with energy for many hours.
Even during long-term fasting, starvation or a very low-carbohydrate diet, the body can produce ketone bodies from dietary fats (15Trusted Source).
Ketone bodies can provide energy for part of the brain, reducing its glucose requirement significantly.
So, during a long fast, the brain can easily sustain itself using ketone bodies and glucose produced from proteins and fats.
It also makes no sense from an evolutionary perspective that we shouldn't be able to survive without a constant source of carbohydrate. If that were true, then humans would have become extinct a long time ago.
However, some people do report that they feel hypoglycemic when they don't eat for a while. If this applies to you, then perhaps you should stick to a higher meal frequency, or at least ask your doctor before changing things.
5) Fasting puts you in "Starvation" Mode
One common argument against intermittent fasting is that it can put your body in "starvation mode." According to the claims, not eating makes your body think it is starving, so it shuts down its metabolism and prevents you from burning fat.It is actually true that long-term weight loss can reduce the amount of calories you burn. This is the true "starvation mode" (the technical term is adaptive thermogenesis) (25Trusted Source).
This is a real effect, and can amount to hundreds of fewer calories burned per day.
However, this happens with weight loss no matter what method you use. There is no evidence that this happens more with intermittent fasting than other weight loss strategies.
In fact, the evidence actually shows that short-term fasts increase metabolic rate.
This is due to a drastic increase in blood levels of norepinephrine (noradrenaline), which tells the fat cells to break down body fat and stimulates metabolism (26Trusted Source, 27Trusted Source).