Intermittent fasting is all about when you eat and not about what you eat. Research studies show that intermittent fasting can help some people lose weight.
But the jury is still out on how sustainable this is in the long term.
In this article, you can find out what the latest research says about intermittent fasting and weight loss.
At ZOE, we know that every body is different and that weight loss can be challenging. Before you embark on a weight loss journey, talk to a healthcare professional to find your healthy weight range.
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What is intermittent fasting?
People who practice intermittent fasting switch between periods of eating and periods of fasting.
There are several different types of intermittent fasting.
Time-restricted eating is one common approach. This form of intermittent fasting extends the period of fasting that naturally happens when you sleep.
For example, you could eat during an 8-hour time window — between 9 a.m. and 5 p.m. — and then fast for 16 hours — until 9 a.m. the next day. This is called 16/8 time-restricted eating.
Other versions of time-restricted eating include 18/6, where you eat during a 6-hour window, and 20/4, which would see you limit your food intake to a 4-hour window.
Alternate-day fasting (ADF) involves fasting for a whole day at a time, followed by eating normally on the next day. You would then repeat this pattern.
Another type of intermittent fasting is the 5:2 diet. It entails eating between 500 and 800 calories on 2 days per week and eating normally the rest of the time.
Intermittent fasting and weight loss research
Intermittent fasting is a relatively new topic of research. At the moment, there isn’t a clear consensus on how effective it is for weight loss in the long term.
One systematic review from 2020 looked at 27 trials that investigated intermittent fasting for weight loss in people who had overweight or obesity.
The researchers found that, on average, participants who followed intermittent fasting lost 4.3% percent of their starting weight after 2–12 weeks.
Of the 27 studies, 12 compared intermittent fasting with traditional, calorie-restricted diets and found similar weight loss results between both approaches.
Another systematic review of 11 studies that involved people with obesity and overweight also compared intermittent fasting with calorie-restricted diets for weight loss.
The majority of the studies — nine of the 11 — found no significant difference in weight loss between intermittent fasting and calorie restriction.
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There is some evidence that when people follow intermittent fasting, particularly time-restricted eating, they eat less, even if they aren’t instructed to do so. This may support weight loss.
One of the largest and longest studies so far involved 332 adults with overweight or obesity, who followed either a 5:2 diet or a calorie-restricted diet.
After a year, both groups had lost around 11 pounds (5 kilograms), and the 5:2 diet was as successful as the calorie-restricted diet.
There were no differences in other health measures between groups, and the drop-out rates were similar.
Is it sustainable in the long term?
Some types of intermittent fasting are harder to stick with for long periods of time than others.
Following time-restricted eating isn’t any more challenging than following traditional weight loss diets. Research suggests that fasting for a 16-hour time window is the most achievable method to support weight loss.
Many people find alternate day fasting harder to follow.
One study involving people with obesity compared a calorie-restricted diet, where participants ate 75% of their energy needs, with a modified ADF diet, where participants alternated days of eating 25% and 125% of their energy needs. The study lasted for a year.
Even when eating the same amount of food overall, those in the ADF group stopped following the plan earlier than those eating a regular diet.
In fact, the researchers found that those on the ADF schedule ate more than recommended on fasting days and less on eating days. Meanwhile, those following consistent daily calorie restriction were more likely to stick to their diet plan.
Regardless, both groups lost a similar amount of weight and had the same changes in health markers.
Another study compared the 5:2 diet with the paleo and Mediterranean diets across 1 year. All of the diets were challenging to follow, but the paleo diet seemed to be the hardest.
Most people following 5:2 reported fasting the recommended 2 days per week. But relatively few people managed to meet the calorie targets.
However, those following intermittent fasting lost the most amount of weight after a year compared with the other diets.
Should you try it?
So far, the evidence indicates that intermittent fasting can be a safe and effective option for weight loss, at least in the short term.
It doesn’t lead to more weight loss than traditional calorie-restricted diets. But, if it suits your lifestyle better, it could be a good option to try.
Importantly, much of the research highlights that different diets suit different people.
Aside from weight management, changing when you eat may also benefit your health in other ways. Research has found links between intermittent fasting and improved heart health and better blood sugar control.
It’s important to remember that intermittent fasting only addresses when you eat, not what you eat.
For your overall health, it’s important to eat a nutritious, diverse, and balanced diet. Aim to include a diverse range of nutrient-dense foods like vegetables, fruit, grains, legumes, nuts, and seeds, as well as healthy fats like extra virgin olive oil.
There are many variations of intermittent fasting, including time-restricted eating, alternate day fasting, and the 5:2 diet.
Currently, the research shows that intermittent fasting can help with weight loss, to a similar degree as conventional calorie-restricted diets.
Some types of intermittent fasting, like alternate day fasting, can be particularly difficult to maintain in the long term.
What’s most important is whether intermittent fasting works for you and your long-term health goals. To support your health when you're not fasting, it’s important to eat a nutritious diet.
The ZOE at-home test analyzes your blood sugar and blood fat responses, as well as the microbes in your gut.
With your personalized ZOE program, you learn how to eat for your body and your long-term health and weight goals.
Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults: a randomized clinical trial. JAMA Internal Medicine. (2017). https://jamanetwork.com/journals/jamainternalmedicine/article-abstract/2623528?redirect=true
Effectiveness of intermittent fasting and time-restricted feeding compared to continuous energy restriction for weight loss. Nutrients. (2019). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836017/
Intermittent fasting and weight loss: systematic review. Canadian Family Physician. (2020). https://pubmed.ncbi.nlm.nih.gov/32060194/
Intermittent fasting, Paleolithic, or Mediterranean diets in the real world: exploratory secondary analyses of a weight-loss trial that included choice of diet and exercise. American Journal of Clinical Nutrition. (2020). https://pubmed.ncbi.nlm.nih.gov/31879752/
Research on intermittent fasting shows health benefits. (2020). https://www.nia.nih.gov/news/research-intermittent-fasting-shows-health-benefits
Time-restricted eating for the prevention and management of metabolic diseases. Endocrine Reviews. (2022). https://academic.oup.com/edrv/article/43/2/405/6371193