The benefits of intermittent fasting are all over social media: faster fat loss, a sharper brain, even a longer life. Some of these claims have real science behind them, and others come mostly from studies on mice and rats. Before you change when you eat, it helps to know which is which.
The short version: in people, intermittent fasting works about as well as other ways of eating less, and for some it is simply easier to stick to. It can modestly improve blood sugar markers. But the bigger promises, such as preventing cancer or Alzheimer’s disease or extending human lifespan, are not proven. It is also not suitable for everyone.
I’m Marko Vuleta, a personal trainer and founder of trainersdubai.com. I use fasting windows with some clients and advise others against them, so here is the evidence I actually rely on.
What is intermittent fasting?
Intermittent fasting is an eating pattern that alternates periods of eating with periods of fasting. It tells you when to eat, not what to eat.
| Pattern | How it works | Notes |
|---|---|---|
| Gentle time-restricted eating (12:12 or 14:10) | You eat within a 10 to 12 hour window and fast overnight | The easiest to maintain |
| 16:8 | You eat within an 8 hour window and fast for 16 hours | The most popular version |
| 5:2 | Eat normally on five days, and eat much less on two non-consecutive days | Needs care on low-intake days |
| Alternate-day fasting | Alternate normal days with fasting or very low-intake days | The hardest to sustain |
How strong is the evidence? A quick guide
| # | Claim | Evidence in humans | Verdict |
|---|---|---|---|
| 1 | Changes cells, genes and hormones | Mostly mechanistic | Real biology, unclear practical impact |
| 2 | Helps weight loss | Randomised trials and reviews | Works through lower intake, not better than other diets |
| 3 | Improves insulin resistance | Small trials | Promising but modest |
| 4 | Reduces oxidative stress and inflammation | Small studies | Limited |
| 5 | Supports heart health | Small trials, mixed signals | Mixed |
| 6 | Triggers autophagy | Cells and animals | Not shown in humans |
| 7 | May help prevent cancer | Animals, early human data | Unproven |
| 8 | Good for your brain | Mostly animals | Unproven |
| 9 | May help prevent Alzheimer's | Animals, one tiny uncontrolled report | Unproven |
| 10 | May extend lifespan | Rodents | Unproven in humans |
1. Intermittent fasting changes how your body uses fuel
When you go without food for many hours, insulin falls, your body shifts from using glucose toward using stored fat and ketones, and cells switch on stress-response pathways. This is described in detail in a New England Journal of Medicine review by de Cabo and Mattson, who call it metabolic switching.
The version you often see online goes further: growth hormone rising fivefold, or metabolism speeding up by up to 14%. Those figures come from fasts lasting a day or more, not from skipping breakfast. A rise in growth hormone during a fast also does not mean you build muscle.
Evidence: well-described biology. It’s real, but it doesn’t automatically translate into better health outcomes from a 16:8 routine.
2. Intermittent fasting can help you lose weight, but it isn't magic
Skipping meals usually means eating less overall, and that is how it works. The newest evidence is clear about it.
A Cochrane review published in February 2026 pooled 22 randomised trials with almost 2,000 adults who were overweight or had obesity. It found little to no difference in weight loss between intermittent fasting and regular dietary advice, or compared with no intervention. The authors also noted that the trials were short and the evidence on side effects is uncertain.
Individual trials say the same:
In the TREAT trial, 116 adults followed either 16:8 eating or three regular meals a day. After 12 weeks, 16:8 produced no greater weight loss, and the fasting group showed a larger drop in lean mass index. In a 12-month trial published in the NEJM, people on a calorie-restricted diet lost 8.0 kg with an 8-hour eating window and 6.3 kg without one, a difference that wasn’t statistically significant. An earlier review of randomised trials found that 9 of 11 studies showed no difference between intermittent and continuous restriction.
What this means for you: if a fasting window makes it easier for you to eat less, it can work. If it makes you binge later or feel miserable, a regular eating pattern is just as effective. Keep strength training and enough protein in your plan, because the lean mass finding is a reason to protect your muscle. See my 10 strength training rules and sleep and fat loss.
Evidence: moderate to strong, and it shows no advantage over other approaches.
3. It may improve insulin resistance and blood sugar
Several short human studies report lower fasting insulin and modest improvements in blood sugar markers during intermittent fasting, particularly when it is combined with weight loss. The commonly quoted numbers (3 to 6% lower glucose, 20 to 31% lower insulin) come from small trials of short duration.
There are important caveats. Results for women are mixed, and one older study found worse blood sugar control in women after about three weeks of alternate-day fasting. And if you have diabetes and take insulin or other glucose-lowering medication, fasting can cause dangerous low blood sugar, so never start without your doctor.
Evidence: limited to moderate. Promising, but not a replacement for medical treatment.
4. It may reduce oxidative stress and inflammation
Some small studies show changes in markers of oxidative stress and inflammation during fasting. These are lab markers, though, and it isn’t clear that they translate into fewer diseases. Treat this as an interesting finding rather than a proven benefit.
Evidence: limited.
5. Effects on heart health are mixed
Some trials show improvements in blood pressure, cholesterol and triglycerides during intermittent fasting, but much of that may come from the weight loss itself.
There is also a warning signal. A preliminary analysis presented at the American Heart Association in 2024 linked eating within less than 8 hours a day to higher cardiovascular mortality. It was an observational abstract that had not been peer-reviewed, and many experts pointed out that it could be explained by other factors, so it doesn’t prove that fasting is harmful. But it is a good reason to be cautious about very short windows, especially if you already have heart disease.
Evidence: mixed. Long-term effects in humans are still unknown.
6. Fasting triggers cellular "clean-up" (autophagy)
Autophagy is the process by which cells recycle damaged components. Fasting does increase it in cells and animals, which is where the claim comes from. In people, autophagy is hard to measure, and nobody has shown that a daily fasting window protects against disease through this route.
Evidence: animal and cell studies only.
7. Can fasting help prevent cancer?
There are interesting animal findings, and early research on fasting around chemotherapy. In humans, there is no proof that intermittent fasting prevents cancer. If you are being treated for cancer, don’t fast without talking to your oncologist, because malnutrition and weight loss can be dangerous during treatment.
Evidence: unproven in humans.
8. Is it good for your brain?
Rodent studies show higher levels of BDNF (a protein involved in nerve cell health) and some protection after stroke. Human trials are limited and have not shown a clear cognitive benefit.
Evidence: mostly animal studies.
9. Can it prevent Alzheimer's disease?
No. There is animal research, and one often-cited report of ten people whose symptoms improved on a program that changed many lifestyle factors at once. It had no control group and could not separate fasting from everything else, so it isn’t evidence that fasting prevents or treats Alzheimer’s.
Evidence: unproven. If you are worried about dementia, the best-supported steps are regular exercise, good sleep, blood pressure control and staying socially active.
10. Will it help you live longer?
In some rodent studies, animals on alternate-day feeding lived dramatically longer. That finding has not been shown in humans, and no trial has tested whether intermittent fasting extends human lifespan.
Evidence: unproven in people.
Who should not try intermittent fasting?
Check with a doctor first, or avoid it, if you are pregnant or breastfeeding, under 18, underweight, take medication for diabetes or other conditions, have gallbladder or digestive problems, or are an older adult at risk of losing muscle.
Be especially careful if you have, or have had, an eating disorder. Strict fasting windows can trigger bingeing and an unhealthy relationship with food. If you notice a preoccupation with food, guilt after eating, or episodes of losing control, stop and talk to a professional.
If you fast for religious reasons such as Ramadan, speak to your doctor about your medication and training during that period.
How to try it sensibly
Start gently. Extending your overnight break to 12 or 13 hours is a low-risk start, and you can adjust from there if it suits you. Fill your eating window with protein, fibre and enough overall food, drink water, and keep sleeping well. Keep training: strength sessions protect muscle, and you don’t have to train fasted (there’s no proven performance benefit). If you feel dizzy, weak or irritable, or your training suffers, change the plan. For structure around training, read my guides on full body vs split training and the components of fitness. Weekend eating habits also affect results: see weekend weight gain.
Frequently asked questions
Does intermittent fasting work for weight loss?
It can, because you may eat less, but trials show it isn’t better than other diets. The best approach is the one you can keep.
What is the best intermittent fasting schedule?
There isn’t one. A gentle 12 to 14 hour overnight break is the easiest to maintain. Choose what fits your day, training, and sleep.
Can I drink coffee while fasting?
Water, plain coffee and unsweetened tea contain almost no calories and are commonly used during fasting windows. Added sugar or milk breaks the fast in the calorie sense.
Does intermittent fasting slow your metabolism?
Evidence is limited. In practice, large drops in metabolic rate are linked more to losing weight and cutting calories than to the timing of meals.
Is it safe for women?
Many women use it without problems, but data are mixed and some small studies suggest differences. Pay attention to your cycle, energy and mood, and talk to a doctor if you are pregnant, breastfeeding or have a history of disordered eating.
Can I exercise while fasting?
Many people do light to moderate training fasted. There is no proven performance advantage, and hard sessions often go better after a meal.
Final thoughts
The honest summary of the benefits of intermittent fasting: it is a tool, not a miracle. It may suit you if it simplifies your eating, and the metabolic effects are modest and promising. The bigger claims about cancer, the brain and lifespan are still hypotheses. Make decisions based on your health, your training, and how you feel.
If you’d like a plan built around your goals and schedule, take a look at my nutrition plans, my personal training in Dubai, the benefits of working with a personal trainer, or get in touch. For more articles like this, browse the blog.
About the author: Marko Vuleta is a certified personal trainer with a degree in Sports Science from the Faculty of Sport in Novi Sad, with NASM and REPs UAE credentials. He is the founder of trainersdubai.com and trains clients in Dubai.
This article is for educational purposes and does not replace medical advice. Consult a doctor before changing your eating pattern, especially if you have a medical condition or take medication.
Sources
- Garegnani LI et al. Intermittent fasting for adults with overweight or obesity. Cochrane Database Syst Rev, 2026.
- Lowe DA et al. Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med, 2020.
- Liu D et al. Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med, 2022.
- de Cabo R, Mattson MP. Effects of intermittent fasting on health, aging, and disease. N Engl J Med, 2019.
- Intermittent fasting and time-restricted feeding compared to continuous energy restriction for weight loss (review of randomised trials). Obesity, 2019.
- American Heart Association. 8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death (preliminary abstract), 2024.
