Is intermittent fasting really the fountain of youth? Here's what the science says

From weight loss to longevity, the list of intermittent fasting’s evidence-based benefits keeps growing. And the best part is you don’t have to go hungry! 

By Sabrina Rogers-Anderson

With countless influencers spruiking the benefits of intermittent fasting - or IF for those in the know - you’d be forgiven for thinking it’s just another flash-in-the-pan diet fad.

But an ever-growing body of scientific evidence shows that alternating periods of eating with periods of fasting can improve a range of health markers and increase our lifespan.

If steering clear of sustenance for hours at a time sounds like a special form of torture, here’s some good news: if you do IF right, you don’t have to go hungry. 

Here’s everything you need to know:

Science-backed benefits of intermittent fasting

A major review of the existing research on intermittent fasting published in eClinicalMedicine in April 2024 found that IF is associated with favourable outcomes supported by high-quality evidence.

Intermittent fasting was shown to reduce:

• Fat mass
• Waist circumference
• Fasting insulin levels 
• LDL (bad) cholesterol 
• Total cholesterol
• Blood pressure 
• Triglycerides

Improving these health markers reduces the risk of a wide range of health conditions, including obesity, high blood pressure, heart disease, type 2 diabetes and some forms of cancer. 

IF was also found to increase HDL (good) cholesterol and fat-free body mass, which includes muscle mass.

Another 2021 review of the effects of IF on the brain found that it has beneficial effects on the symptoms and progression of neurological disorders including epilepsy, dementia and multiple sclerosis.

The risks of intermittent fasting and who should avoid it

While there isn’t much solid evidence on the ill effects of IF, there have been some reports of hypoglycaemia (low blood sugar), weakness and dizziness. If you don’t eat enough protein, fasting can also lead to muscle wasting.

Fasting may also be dangerous for certain groups of people. Young children, pregnant and breastfeeding women, older adults, and people with hormone imbalances, immune deficiencies, dementia or a history of eating disorders should avoid it.

If you have any doubts about whether fasting is suitable for you, talk to your GP. 

The best fasting protocol for health and longevity

With so many different types of intermittent fasting out there, which one should you choose? 

The terminology can seem confusing, but time-restricted eating, 3-day-fasting, circadian eating, and the 5:2 and 16:8 diets are all different forms of IF that prescribe varying windows of eating and fasting.

Many experts, including Ioannis Nezis, a UK cell biology researcher who studies the cellular effects of fasting, are fans of the 16:8 method. This involves eating during an 8-hour window and fasting for the remaining 16 hours.

Larisova also recommends an 8 to 10-hour eating window in line with our circadian rhythms - known as circadian eating.

“Research shows that this is the best method for most people and that living in tune with our circadian rhythms is really good for our health,” she explains. “Our parents told us to eat breakfast like a king, lunch like a prince and dinner like a pauper, and they were right.

“Your body should be in a fasted state at night to increase your autophagy [the process of clearing out damaged cells] and your production of NAD+ [a coenzyme that plays a critical role in fighting disease and healthy ageing]. If you go to sleep with a full stomach, the thermic effect of food makes you hot and disturbs your deep sleep. There are many factors that indicate we should adopt a circadian eating pattern.”

Here are Larisova’s top circadian eating tips:

• Don’t eat or drink anything other than water for at least an hour after waking in the morning.
• Eat a protein and carbohydrate-rich breakfast at the same time every day to regulate your circadian rhythm.
• Have dinner at least 2 hours before bedtime. It should include protein and non-starchy vegetables.
• Walk for 30 minutes after dinner.
• Stick to the 8 to 10-hour eating window.

Does intermittent fasting cause heart disease?

A study abstract that was recently presented at an American Heart Association conference claimed that IF can increase the risk of death from heart disease. The media ran the story with shock headlines about the dangers of fasting and caused widespread fear.

But the controversial new study of 20,000 US adults has several limitations, says nutritionist, exercise physiologist and co-founder of Chief Nutrition Veronika Larisova. To start, it hasn’t yet been peer-reviewed (analysed by other experts in the field as a form of quality control) or published.

“The major problem with this research is that it says an eating window of less than 8 hours [per 24 hours] increases the risk of heart disease mortality, but most of the [previous] studies recommend an eating window of 8 to 10 hours,” Larisova explains.

“Less than 8 hours makes a lot of people overeat because they think they will be hungry later or undereat because they don’t have enough time. The goal with intermittent fasting isn’t to eat more or less calories, it’s to eat them in a smaller window.”

Another issue is that the participants’ eating windows were self-reported on two occasions that were then used to extrapolate their eating patterns over the course of the eight-year study. 

“People don't remember or don't like to disclose what they eat,” says Larisova. “Some people binge eat, eat junk food or binge drink alcohol and feel ashamed about it, so they won't disclose it.

“Also, did they overeat or undereat in the eight-hour window? What was their diet in general? Was it a healthy, balanced diet that contained vitamins and minerals or were they fasting and then eating ultra-processed foods? Even if they thought they were eating healthy, vegetable and seed oils can increase the risk for heart attack and many foods have hidden sugar and preservatives.

“Finally, what was their health like to start with? Whether they had obesity or underlying health conditions also wasn't stated. There are too many issues with this study.”

The bottom line

It’s always a good idea to talk to your doctor before starting a new eating plan, but the evidence shows that intermittent fasting remains safe for most healthy people.