Fasting — not eating for a period of time — has been practised by humans for millennia, with reasons ranging from religious rites and treatment of disease to political protest, or from necessity during famine. The “eat less, live longer” idea is a more recent one, originating from experiments in rats conducted during the 1930s that showed restricting the diet of these animals extended their lifespan. Today, fasting is presented as a recipe for better health and longevity, acting through multiple biological mechanisms. One of these mechanisms — autophagy — has attracted lots of attention recently, so we thought we’d break down what autophagy is and its link to the health and longevity effects of fasting.
Firstly, what is autophagy?
Autophagy translates to “self-eating”. It’s a cell’s way of breaking down and recycling damaged proteins and other cellular material so it can function more efficiently. Autophagy is associated with the proper maintenance of tissues and cells in the body. This normal housekeeping process keeps cells resilient and has been linked to healthy ageing in research on animals. Autophagy naturally declines with age, and this drop is linked to the accumulation of damaged cellular contents and an increased risk of age-related conditions.
What is fasting? And what are the evidence-based benefits?
Fasting encompasses a range of eating patterns in which food intake is limited for set periods, from overnight fasting windows to more structured approaches such as time-restricted eating (e.g., 16:8, which involves eating within an eight-hour window and fasting for 16 hours) and the 5:2 diet (eating normally for five days of the week and fasting for two days).
Clinical trials show that fasting can help with weight loss, improve insulin sensitivity, and reduce heart disease risk, but these benefits typically occur because people follow better diets rather than because of any unique features of fasting. Fasting can be a helpful tool for some individuals, but it is not inherently superior to other well-established, sustainable nutrition strategies, such as portion control and reduced calorie intake.
Part of fasting’s appeal comes from its simplicity and structure. For many men, the idea of skipping breakfast or not eating after 6pm feels easier to stick to than reducing calories or adjusting portions. Fasting offers a sense of control and measurable progress, which can be motivating. Nevertheless, most studies are relatively short-term, and many benefits appear to be linked to overall energy reduction rather than to fasting itself. The evidence is promising, but fasting is not a magic bullet.
Fasting and autophagy
Because low energy availability and nutrient deprivation can trigger autophagy, fasting has become a key talking point.
Small studies of humans suggest that longer fasts may activate autophagy-related markers, but we still do not know for how long or how often people need to fast for a meaningful effect on autophagy, or whether it translates into better long-term health or slower ageing.
Meanwhile, it is worth noting that regular exercise, adequate sleep, and healthy, balanced eating all support proper cellular function, even if they do not directly increase autophagy as fasting might.
Fasts lasting three to five days periodically surge in popularity. These trends promote water-only fasting as a form of metabolic or cellular “reset”. While prolonged energy deprivation appears to increase the processes that underpin autophagy in animal studies, robust evidence from humans is scarce. Some research suggests that any metabolic changes observed during extended fasting tend to return to baseline once normal eating resumes, casting doubt on long-term benefits. Extended fasts can also carry harmful side effects, including fatigue, dizziness, electrolyte imbalance, muscle loss, impaired concentration, and disrupted blood glucose regulation. In my experience, these risks outweigh any potential benefits suggested by the current evidence.
Should you fast?
While fasting can offer some benefits, it’s not the only available tool in your toolkit. A more practical approach is to focus on mindful eating: paying attention to hunger and fullness cues, enjoying meals without guilt, and letting your body’s natural rhythms guide when and how you eat. Supporting your health doesn’t require extreme fasting; instead, creating consistent, balanced habits that suit your lifestyle often has a bigger and more sustainable impact than chasing the latest dietary trend.
Further, building meals around lean proteins, including plant foods such as soy foods, beans, and lentils, helps with satiety and supports muscle health. Hitting the recommended daily serves of fruit and vegetables adds fibre, antioxidants, and a whole suite of nutrients that your body thrives on. And limiting sugary foods, pastries, processed meats and alcohol can make a real difference to energy balance and overall wellbeing without feeling restrictive. These steady, routine habits can be far easier to follow.
Are there risks or limitations? Who shouldn’t fast?
Fasting isn’t suitable for everyone. Restricting food for long periods can lead to low energy, irritability, headaches, and difficulty concentrating, especially when someone is juggling work, training, or family commitments. In practice, I have seen this approach backfire, with men compensating by eating too much later in the day, resulting in indigestion and a calorie surplus that can cause weight gain. Another concern is that fasting can become another rigid food rule, which may undermine someone’s relationship with food rather than support it.
There are men for whom fasting simply isn’t a good fit. Anyone with a history of disordered eating, compulsive dieting or a rocky relationship with food should steer clear, as fasting can easily trigger old behaviours. Men living with diabetes who use insulin or glucose-lowering medications (e.g. sulfonylureas) also run the risk of hypoglycaemia when they restrict food or go long periods without eating. Teenagers, older men (i.e. those aged over 65 years) who are underweight or losing weight unintentionally, and men dealing with chronic illness should prioritise regular, balanced meals. As with any nutrition approach, the best and safest option is to tailor it to your own needs and health goals, so consult a dietitian or doctor for specific advice.
Is there a better diet for longevity?
As the science currently stands, the best recipe for a long and healthy life is still the simple, unsexy stuff: plenty of plants and fibre, adequate protein, exercise and strong social connections.
Joel Feren
Accredited Practising Dietitian and Accredited Nutritionist
Known as The Nutrition Guy, Joel Feren is an Accredited Practising Dietitian and Accredited Nutritionist with a background in biomedical sciences. His speciality area is men’s health. Joel works alongside the media and some of the biggest food brands in the industry and is helping to shape the current food landscape and nutrition conversation.
