According to a major review published yesterday, intermittent fasting is no better for weight loss than the traditional dieting style of cutting calories daily. Researchers analysed 22 global studies and found that people who were overweight or who had obesity lost as much weight by continuous energy restriction as by following alternate-day fasting and time-restricted eating. Headlines such as “5:2 diet not a miracle solution’’ followed.
I would say that it’s certainly an interesting study, and it pools together all forms of fasting under a single umbrella. For instance, it includes alternate-day, periodic and time-restricted eating (TRE) studies. And TRE — the most common fasting intervention included (in 10 out of the 22 studies) — can have more modest effects on weight compared with other forms of fasting.
That said, my belief is that with any diet — whether the 5:2, or a traditional method of continuous energy restriction — the best is the one that suits you. Fasting is not for everyone. But both intermittent fasting and continuous calorie restriction are effective and valid routes to losing weight.
It’s true that there’s conflicting evidence out there. Some research suggests that the 5:2 — a diet popularised by Dr Michael Mosley, my dad, isn’t as effective as what you would class as a traditional diet.
However, there’s also a lot of evidence to say that it is an effective form of dieting. Another recent meta-analysis in 2025 looked at only one type of fasting — the 5:2. This big study was made up of over 20 randomised control trials with almost 1,400 people. It found that the 5:2 diet significantly reduces body weight, body mass index, waist circumference and body fat percentage. It also significantly reduced a range of cardiovascular markers, including LDL cholesterol (the bad cholesterol) and blood pressure.
The study found that it was safe and tolerable, with only mild symptoms reported. This was when compared with control groups, who were often advised to continually restrict their calories.
Initially, my dad used it to reverse his own type-2 diabetes, lose weight, and keep it off. When he was at university he was pretty slim but, like many people, he gradually put on a little bit of weight every year — half a kilo, a kilo — to the point where by the time he reached his fifties, he was overweight and had developed type-2 diabetes.
Dr Michael Mosley
NICK HOLT/CHANNEL 4
At that time, back in 2012, it was only just being considered that diabetes was reversible by losing weight through a dietary approach. My dad made a BBC programme with Horizon, Eat, Fast, and Live Longer, where he followed this new way of eating called intermittent fasting. And essentially, he adapted this into the 5:2 diet, where he’d eat normally for five days a week and really restrict his energy intake to 500 or 600 calories for two non-consecutive days a week.
The concept of intermittent fasting is based on the fact that the body is in a state of either growth or repair mode. And in our modern life, we’re constantly in growth mode, because we’re constantly fuelling our bodies with calories. When you are fasting, you then switch into repair and clean-up mode, known as autophagy.
The other key concept behind fasting and the 5:2 is that on those fasting days you burn off the glycogen stored in your liver and also in muscles — that is, you burn off that carbohydrate and sugar — and go into ketosis and fat-burning mode.
Consequently, my father was able to lose more than 9kg in weight and reverse his type-2 diabetes. He remained in good health thereafter and kept the weight off long-term by occasionally dipping back into doing a fast day here and there. What also helped was that he improved the quality of his nutrition by following a Mediterranean-style diet.
• How to cheat the Mediterranean diet (when you’re back home)
He really did spark this global phenomenon where lots of people started doing the 5:2 diet around the world, from politicians, to celebrities — the US chat show host Jimmy Kimmel said he was doing the 5:2 after watching the programme — and normal people. I regularly meet people who’ve seen massive benefits from following the 5:2 and have lost lots of weight.
Does fasting also affect longevity? While more research is needed in humans, animal studies show that calorie restriction can extend lifespan. The reasons for this have been linked to autophagy, reduced inflammation and improved mitochondria (the power stations of the cell). And fasting is said to mimic some of these calorie restriction benefits, and can improve cardiometabolic markers in humans, such as insulin sensitivity, inflammation and cholesterol.
But importantly, some people find this approach much easier and more doable than continuous energy restriction, as they’re not having to think about what they’re eating day in day out. Because that does take a toll.
We only have so much willpower, so it can become harder to do over the long term. We used to think that slow and steady wins the race, but one of the reasons that many people give up on a traditional diet is that when you’re eating only slightly less each day, it’s less motivating because you’re not seeing such rapid results.
My book, Food Noise, is about the GLP-1 weight loss medications, the best approach to follow while you’re taking them — and after you come off them. Your “food noise’’ can come rushing back and so it’s important to consider what you’ll do when that happens — and following the 5:2 is one of my suggestions.
• Read more expert advice on healthy living, fitness and wellbeing
This has been echoed by Susan Jebb, the professor of diet and population health at the University of Oxford. She released an academic review about the rapid weight regain after coming off GLP-1s compared to after traditional dieting and mentioned the 5:2 as an option for weight-loss maintenance.
The 5:2 gives people a bit more agency and control than traditional dieting methods. People also tell me that it’s given them more understanding about what to eat — what foods are filling for them, and which are empty calories.
Many have reversed their diabetes and dramatically changed their lives. So many people have managed to come off blood-pressure medication, reduce their cholesterol and even reverse their diabetes. It has been fantastic for a lot of people. It has helped hundreds of thousands across the globe.
As told to Anna Maxted
Food Noise: How Weight-Loss Medications & Smart Nutrition Can Silence Your Cravings by Dr Jack Mosley (Short Books, £16.99). To order a copy go to timesbookshop.co.uk. Free UK standard P&P on orders over £25. Special discount available for Times+ members