Is intermittent fasting safe?
As with anything, intermittent fasting is safe for the right people. Around 50 studies of intermittent fasting have been performed in rodents, and about 40 studies have been performed in humans. Of these studies, only one to date has reported negative effects of intermittent fasting. And this was found in rodents only. Studies in humans routinely demonstrate heart-healthy benefits of intermittent fasting. For example, things like reductions in cholesterol, blood pressure, glucose and improvements in insulin sensitivity.
There are, however, some groups of people for whom intermittent fasting isn’t considered safe. Those groups are:
- Women who are pregnant, planning to get pregnant or breastfeeding
- Anyone with an eating disorder, a history of or a predisposition to eating disorders
- Those with a BMI of below 20 or people who are underweight
- Anyone who has been diagnosed with Type 1 Diabetes, unless under a doctor’s supervision
- People younger than 18 years old
Important note: If you have any medical conditions or are taking prescription medication, we highly recommend speaking with your physician. Especially prior to commencing any new diet, eating or exercise regime.
Is intermittent fasting safer than calorie restriction?
What’s the difference between intermittent fasting and calorie restriction?
The difference is fairly simple. Calorie restriction, otherwise known as caloric restriction, relies upon daily calorie restriction. One adheres to a continuous regime of somewhere between 1200-1800 calories per day, with very little variation. Whereas with intermittent fasting, one fasts for several hours a day or several days a week. And then takes the rest of the time off.
Intermittent Fasting expert and world-renowned author of The Obesity Code, Dr Jason Fung explains the difference. It’s the difference between average and frequency, he explains through metaphor… “The weather in Death Valley, California should be perfect with a yearly average temperature is 25 Celsius. Yet, most residents would hardly call the temperature idyllic. Summers are scorching hot, and winters are uncomfortably cold.”
Averages only tell part of the story
“You can easily drown crossing a river that, on average, is only two feet (60cm) deep. If most of the river is one foot (30cm) deep and one section is ten feet (3 metres) deep, then you will not safely cross. Jumping off a one-foot wall 1000 times is far different than jumping off a 1000-foot wall once.”
“In a week’s weather, there is a huge difference between having seven grey, drizzling days with one inch of rain each. And having six sunny, glorious days with one day of heavy thunderstorms and showers.”
“It’s obvious in all these examples that overall averages only tell one part of the tale, and often, understanding frequency is paramount. So why would we assume that reducing 300 calories per day over one week is the same as reducing 2100 calories over a single day? The difference between the two is the knife-edge between success and failure.”
Translation? Reducing some of your calorie intake every day is completely different to fasting intermittently. And they have very different results.
The New Research
In this new study, published in Cell Metabolism in August, researchers studied 60 participants. These participants enrolled for four weeks and randomised to either an ADF (or Alternate Day Fasting) group or an ad libitum control group. The latter of which could eat as much as they wanted. The researchers chose Alternate Daily Fasting because they said it was one of the most “extreme dietary interventions” and they didn’t feel it had “been sufficiently investigated within randomized controlled trials.”
Participants in both groups were all of normal weight and healthy. To make sure that the people in the ADF group didn’t take in any calories during fasting days, researchers monitored their glucose. They also asked the participants to fill in diaries documenting their fasting days.
The researchers also studied a group of 30 people, in addition. This group had already practiced more than six months of strict ADF previous to the study enrollment. They compared this group to normal, healthy controls with no fasting experience. For this ADF cohort, the main focus was to examine the long-term safety of the intervention.
What were the study’s conclusions about the safety of intermittent fasting?
“We found that on average, during the 12 hours when they could eat normally, the participants in the ADF group compensated for some of the calories lost from the fasting, but not all,” says Harald Sourij, a professor at the Medical University of Graz. “Overall, they reached a mean calorie restriction of about 35%. And lost an average of 3.5 kg [7.7 lb] during four weeks of ADF.”
They also found the following:
- Participants showed increased circulation of ketone bodies, even on nonfasting days. This has been shown to promote health in various contexts.
- Partipants had reduced levels of sICAM-1, a marker linked to age-associated disease and inflammation.
- They had lowered levels of triiodothyronine without impaired thyroid gland function. Previously, lowered levels of this hormone have been linked to longevity in humans.
- They had lowered levels of cholesterol.
- They had a reduction of lipotoxic android trunk fat mass — commonly known as belly fat.
What do these results mean?
Previously, because it requires people to consume vastly reduced calories on fasting days (or to not consume any calories at all) some people claimed fasting was unsafe. Some research even suggested that calorie-restrictive diets could result in malnutrition and a decrease in immune function. But this new research shows that intermittent fasting has tonnes of associated health benefits. And it doesn’t seem to have any adverse effects when used long-term either. In fact, quite the opposite! Even after six months of ADF, the participants’ immune function stayed stable.
It requires more research to work out the exact mechanisms that control these health benefits. But Frank Madeo, a professor of the Institute of Molecular Biosciences at Karl-Franzens University of Graz in Austria believes it may be down to something in our genes. “The reason might be due to evolutionary biology,” Madeo explained. “Our physiology is familiar with periods of starvation followed by food excesses. It might also be that continuous low-calorie intake hinders the induction of the age-protective autophagy program, which is switched on during fasting breaks.”
And intermittent fasting is simple to do, too
“The elegant thing about strict ADF is that it doesn’t require participants to count their meals and calories. They just don’t eat anything for one day,” said Thomas Pieber, head of endocrinology at the Medical University of Graz.
Have you tried intermittent fasting? Did you notice any health benefits? We’d love to know? And if you haven’t given it a shot yet, why not take our quiz to see which intermittent fasting method is right for you.
Ready to give it a shot? Join the Super Squad here.