Intermittent fasting: benefits and what the studies show about time restricted eating

Intermittent fasting is a way of eating in which you alternate meal periods with long breaks from food, and its most studied form, time restricted eating, means having all of the day's meals within a 6-10 hour window: in a study published in Cell Metabolism, a 6-hour window that ended before 3 pm lowered systolic blood pressure by 11 mmHg and improved insulin sensitivity, without the participants losing weight. In my longevity routine, the eating window starts with a morning ritual: water, natural light and 10 minutes in front of a red light therapy panel. Below you will find what the studies show, where the results are more modest than the internet promises and how to build a window that truly helps you.

What is intermittent fasting?

Intermittent fasting is an eating pattern that sets when you eat, not necessarily what you eat. There are three main forms studied in research:

• Time restricted eating (TRE): you eat every day within a fixed window, usually 6-10 hours, and for the remaining 14-18 hours you drink only water, tea or unsweetened coffee.
• Alternate-day fasting: one day you eat normally, the next day very little (around 500 kcal) or nothing at all.
• The 5:2 variant: five regular days and two days a week with a very low calorie intake.

Researchers Rafael de Cabo and Mark Mattson explained the central mechanism in a review in the New England Journal of Medicine (2019): after roughly 12 hours without food, the liver's glycogen stores drop and the body makes the "metabolic switch" towards burning fat and producing ketone bodies. This switch activates pathways of cellular repair, stress resistance and autophagy, the process through which the cell "recycles" its worn-out components.

What do the studies show about the benefits of intermittent fasting?

The direct answer: intermittent fasting supports blood glucose control, blood pressure and weight, but in most studies the benefits come mainly from the fact that you eat less. The interesting exception is the early window, which seems to bring metabolic benefits of its own.

Sutton and colleagues, 2018 (Cell Metabolism). Men with prediabetes ate for 5 weeks within a 6-hour window, with the last meal before 3 pm, and for 5 weeks within a 12-hour window, with exactly the same calories. On the short, early window, systolic blood pressure dropped by 11 mmHg, diastolic by 10 mmHg, insulin went down and a marker of oxidative stress fell by about 14%. Evening appetite was lower too. All of this without weight loss. The study is small, but it was the first to show that meal timing matters in itself.

Wilkinson and colleagues, 2020 (Cell Metabolism). Nineteen adults with metabolic syndrome, who were eating across more than 14 hours a day, restricted their meals to a 10-hour window for 12 weeks. The results: around 3% of body weight lost, a 4% smaller waist, 11% lower LDL cholesterol and better blood pressure, on top of the medical treatment they were already receiving.

Jamshed and colleagues, 2022 (JAMA Internal Medicine). Ninety adults with obesity followed a calorie-restricted diet for 14 weeks. Half ate between 7:00 and 15:00, the others within a window of 12 hours or more. The early window group lost 6.3 kg, compared with 4.0 kg, had diastolic blood pressure 4 mmHg lower and reported more energy and a better mood.

Does intermittent fasting work for weight loss?

Yes, but no better than a classic diet with controlled calories. Intermittent fasting works because it simplifies your choices and reduces evening snacking, not because it "melts" fat through some magic mechanism.

Lowe and colleagues, 2020 (JAMA Internal Medicine, the TREAT study). 116 overweight adults ate for 12 weeks either three structured meals or between 12:00 and 20:00 (16:8), with no other rules. The weight difference between the groups was only 0.26 kg, not significant. In the subgroup measured in the lab, roughly 65% of the kilograms lost in the 16:8 group were lean mass, which is largely muscle.

Liu and colleagues, 2022 (New England Journal of Medicine). 139 people with obesity followed the same calorie-restricted diet for 12 months, with or without an 8:00-16:00 window. They lost 8.0 kg with the window and 6.3 kg without, a difference that was not statistically significant.

Semnani-Azad and colleagues, 2025 (The BMJ). The largest analysis to date, with 99 randomised trials, confirms the picture: intermittent fasting and classic calorie restriction have similar results, both better than eating without rules. Alternate-day fasting brought on average 1.3 kg more than the classic diet, but most studies lasted under 24 weeks.

My practical conclusion: choose the window that fits your life. If it helps you eat more mindfully and sleep better, it is an excellent tool. If it makes you eat chaotically in the evening, it is not for you.

How long should the eating window be?

For most healthy adults, an 8-10 hour window, started in the morning or at noon and finished 3 hours before bedtime, is a realistic starting point supported by studies.

Window	Example schedule	What the studies show	Who it is for
12:12	8:00-20:00	Healthy baseline; removes night-time snacking	Beginners, anyone
14:10	8:00-18:00 or 9:00-19:00	Better weight, waist, LDL and blood pressure in metabolic syndrome (Wilkinson, 2020)	The best balance between benefits and sustainability
Early 16:8	7:00-15:00	Greater weight loss and lower diastolic blood pressure, with calorie restriction (Jamshed, 2022)	People with a morning schedule and early dinners
Late 16:8	12:00-20:00	No advantage over regular meals, with loss of muscle mass (Lowe, 2020)	Only with enough protein and strength training
Early 18:6	8:00-14:00	Better insulin and blood pressure, without weight loss (Sutton, 2018)	Advanced, with your doctor's approval

Indicative examples for healthy adults. Black coffee, unsweetened tea and water do not break the fasting period.

Is intermittent fasting safe? What the 91% study says

For healthy adults, randomised trials have not shown important adverse effects of time restricted eating. Still, it is not for everyone and it is worth knowing the data that raised concerns too.

In 2024, an abstract presented at an American Heart Association conference reported that people who ate within a window under 8 hours had a 91% higher risk of cardiovascular death. The figure went around the world, but the study was observational, relied on two days of recalled meals, had only 414 people in the short-window group and had not gone through peer review at the time of the presentation. It shows an association worth studying, not proof that fasting harms the heart.

Talk to your doctor before you start if you are pregnant or breastfeeding, if you have diabetes treated with insulin or glucose-lowering medication, if you have a history of eating disorders, if you are under 18 or if you take medication that must be taken with food.

Intermittent fasting after 40: how do you protect your muscle?

After 40, my rule is simple: the time window gets shorter, the protein does not. Fewer meals mean that every meal has to bring enough protein, around 30-40 g, so the muscle receives the signal to build.

The result from the TREAT study, with a large loss of lean mass, appears precisely when people shorten the window without thinking about protein and without strength training. Muscle is the organ of longevity: it supports blood glucose, bones, balance and VO2 max. I wrote in detail about quantities in the article how much protein after 40, and about the role of training in VO2 max and longevity.

One more detail that makes a difference: the last meal at least 3 hours before bedtime. A late dinner keeps insulin and body temperature high exactly when the brain needs deep sleep to clean itself, a process described in the article on deep sleep and the glymphatic system.

How do you combine intermittent fasting with the morning ritual and red light therapy?

Intermittent fasting works with your biological clock, and the biological clock is set first of all by light and by meal timing. That is why the morning is the moment when I "open" the day: natural light at the window or outside, water, then a first meal rich in protein.

In this ritual, red light therapy has a natural place. Red light therapy (660 nm) and near-infrared light (850 nm) act at the level of the mitochondria, the cell's power plants, and studies from recent years show that red light can also influence metabolism. In a 2024 study, Powner and Jeffery showed that 15 minutes of 670 nm red light on the back, before a glucose tolerance test, reduced blood glucose by 27.7% over the following two hours, and the glucose peak by 7.5%. It is a small study, on healthy adults, but it shows that "illuminated" mitochondria use more glucose.

There are no studies yet that directly combine intermittent fasting with red light therapy, so I am not promising you a cumulative effect. For me, the 10 minutes in front of the panel, on an empty stomach, with black coffee beside me, are the moment when I choose my intention for the day and prepare my body for the first meal. And if you want to see all the research we rely on, we have gathered it on the page red light therapy studies and effects.

Frequently asked questions

What is intermittent fasting?

Intermittent fasting is an eating pattern in which you alternate meal periods with planned breaks from food. The most studied form is time restricted eating, in which you have all of the day's meals within a 6-10 hour window, for example 16:8 or 14:10.

What are the benefits of intermittent fasting?

Studies show that intermittent fasting supports blood glucose control, blood pressure, cholesterol and weight. In a study in Cell Metabolism, a 6-hour window that ended before 3 pm lowered systolic blood pressure by 11 mmHg and improved insulin sensitivity, without weight loss.

Do you lose more weight with intermittent fasting than with a regular diet?

Not clearly. A 2025 meta-analysis published in The BMJ, with 99 randomised trials, shows that intermittent fasting has similar results to a classic calorie-restricted diet. Alternate-day fasting brought on average 1.3 kg more.

Which eating window is best: 16:8 or 14:10?

For most adults, an 8-10 hour window started in the morning and finished at least 3 hours before bedtime is the most realistic. Early windows, with the last meal in the afternoon, brought the best results for insulin and blood pressure.

Do you lose muscle with intermittent fasting?

It can happen. In the TREAT study, roughly 65% of the weight lost in the 16:8 group was lean mass. After 40, combine the time window with 30-40 g of protein per meal and strength training at least twice a week.

Read next

• The complete guide to red light therapy
• How much protein after 40: muscle, the organ of longevity
• VO2 max: the strongest predictor of longevity
• Deep sleep and the glymphatic system

Sources

• de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019;381(26):2541-2551. PubMed
• Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. 2018;27(6):1212-1221. DOI
• Wilkinson MJ, Manoogian ENC, Zadourian A et al. Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome. Cell Metab. 2020;31(1):92-104. PubMed
• Jamshed H, Steger FL, Bryan DR et al. Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial. JAMA Intern Med. 2022;182(9):953-962. DOI
• Lowe DA, Wu N, Rohdin-Bibby L 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;180(11):1491-1499. PubMed
• Liu D, Huang Y, Huang C et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N Engl J Med. 2022;386(16):1495-1504. PubMed
• Semnani-Azad Z et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ. 2025;389:e082007. The BMJ
• Zhong VW et al. 8-hour time-restricted eating and cardiovascular mortality. Abstract presented at the AHA EPI|Lifestyle Scientific Sessions, March 2024 (preliminary data). Abstract and commentary
• Powner MB, Jeffery G. Light stimulation of mitochondria reduces blood glucose levels. J Biophotonics. 2024;e202300521. PubMed
• Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS Biophys. 2017;4(3):337-361. PubMed

This information is for educational purposes and does not replace medical advice. NeuroGenesis DNA red light therapy devices are intended for wellbeing and are not intended to diagnose or treat diseases. Before starting intermittent fasting, talk to your doctor, especially if you have diabetes, take medication, are pregnant or have a history of eating disorders.