Intermittent fasting may not deliver significantly better weight loss results than traditional calorie-controlled diets, and in some cases, may make ''little to no difference' at all, a major global review has found.
The analysis by Cochrane examined 22 studies involving 1,995 adults living with overweight or obesity across Europe, North America, China, Australia and South America.
In its key findings, the review states: “Compared to traditional dietary advice (like restricting calories or eating different types of foods), intermittent fasting may make little to no difference to weight loss and quality of life in adults living with overweight or obesity. We are less sure about the results for unwanted events.”
The researchers evaluated different forms of intermittent fasting, including time-restricted eating, periodic fasting and alternate-day fasting, and compared them to standard approaches such as calorie restriction and balanced dietary changes.
Across 21 studies involving 1,430 people, intermittent fasting showed minimal difference in weight loss compared to traditional dietary advice. When measured against no treatment or being placed on a waiting list, the findings were similar.
“Compared to no advice or being on a waiting list, intermittent fasting likely makes little to no difference to weight loss. We are less sure about the evidence for quality of life, and unwanted events (such as fatigue, headache and feeling sick).”
A growing global concern
The review comes against the backdrop of rising global obesity rates.
“Obesity is a serious medical condition characterised by high body fat, which can cause weight-related complications and may lead to serious illness (like type 2 diabetes) and death. Worldwide obesity levels are growing, increasing the burden on healthcare systems.”
Weight loss, the review notes, “remains the best way to reduce health risks and effects on society associated with overweight and obesity.”
Traditional dietary advice typically involves “reducing calories, and changing eating habits to eat healthier foods or different amounts of protein, carbohydrate and fat.” Intermittent fasting, by contrast, involves alternating periods of eating and fasting.
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The researchers note that intermittent fasting “may improve overall health through helpful changes to some body functions,” but it may also trigger “unwanted events, such as fatigue, headache or nausea.”
Evidence gaps remain
The review highlights important gaps in the available evidence.
None of the included studies reported “people's satisfaction with intermittent fasting, their diabetes status or overall measures of other health problems.”
Researchers acknowledged limitations in the quality of evidence.
“We are moderately confident in the results for weight loss when comparing intermittent fasting with no treatment. However, our confidence is low to very low for our other points of interest because most included studies did not use the most robust methods, they included few people, and reported results that were inconclusive.”
The findings suggest that while intermittent fasting remains popular as a weight-loss trend, its advantages over conventional calorie-controlled diets may be limited, at least based on current evidence.
The review concludes that “we need further research” to better understand its broader health impacts, including diabetes outcomes, quality of life, and long-term safety.
What is intermittent fasting?
Intermittent fasting involves cycling between periods of eating and not eating. Rather than focusing on what foods to consume, it centres on when you eat.
The most widely practised version, the 16:8 method, allows all meals within an eight-hour window, followed by a 16-hour fast. For instance, someone might eat between noon and 8 p.m., then avoid food until the next day. Other popular formats include the 5:2 diet, where individuals eat normally for five days and significantly cut calories on two non-consecutive days, and alternate-day fasting, which alternates between regular eating days and fasting days.
Supporters argue that this pattern mirrors how early humans ate, when food scarcity often meant long gaps between meals. Advocates also point to research suggesting that fasting encourages the body to shift from burning glucose to burning stored fat for energy. This metabolic switch is believed to enhance fat burning, support cellular repair, and reduce inflammation.
Extending the overnight fasting period, in particular, has been associated with better insulin sensitivity, improved blood sugar control, and even longer lifespan in animal studies. Because of these findings, intermittent fasting has gained popularity not just as a weight-loss strategy but as a broader lifestyle approach with potential long-term health benefits.
Cardiovascular risk
Another study has also cast doubt on some of these claims. Researchers examined data from more than 19,000 adults in the United States and found a concerning link between strict intermittent fasting and higher cardiovascular mortality. Individuals who limited their eating to eight hours or less per day had a 135 per cent higher risk of dying from heart-related conditions compared to those who spread their meals over 12 to 14 hours.
Cardiovascular mortality includes deaths caused by heart attacks, strokes, and other disorders affecting the heart and blood vessels. While the study did not find a significant increase in overall mortality, the consistent rise in cardiovascular deaths across age groups, genders, and lifestyle categories stood out. In simple terms, eating within a very narrow window may not reduce overall lifespan, but it could increase vulnerability to serious heart conditions.
The research drew on data from the National Health and Nutrition Examination Survey (NHANES) collected between 2003 and 2018. It followed 19,831 American adults over a median period of 8.1 years. Participants reported everything they ate and drank on two separate days, roughly two weeks apart.
Based on these records, researchers calculated each person’s average daily eating window. Mortality outcomes were tracked through the National Death Index until December 2019.
The findings indicated that those who confined meals to under eight hours daily faced significantly higher cardiovascular risks compared to individuals who ate across 12 to 14 hours.
The risk appeared especially high among smokers, people with diabetes, and those already diagnosed with heart disease. Notably, the results remained consistent even after adjusting for factors such as diet quality, meal frequency, socioeconomic background, and lifestyle habits. The researchers concluded that while the relationship between intermittent fasting and overall mortality is still uncertain, the elevated risk of heart-related deaths warrants attention.
Expert advice
Dr Rajeshwari Panda, Head of the Dietetics Department at Medicover Hospital, Kharghar, Navi Mumbai, advises caution in interpreting the latest findings.
“This is an observational study. So while the headline sounds scary, more research is needed before we can firmly conclude that intermittent fasting directly causes harm,” she explained, in a recent conversation with the First Check.
According to her, intermittent fasting can offer certain advantages. “It can support weight loss, help regulate blood sugar, improve metabolic markers, and even curb emotional or late-night eating habits,” Dr Panda said. However, she added that such benefits are generally observed in the short term.
She also warned that fasting within very narrow time frames carries potential downsides. Prolonged restriction may result in fatigue, headaches, weakness, and muscle loss. Long-term evidence remains inconclusive, and an extremely short eating window, such as eight hours, may lead to inadequate nutrient intake, disordered eating behaviours, or hormonal imbalances.
She added that humans have always fasted naturally in the past: “Traditionally, our ancestors often went 10 to 12 hours without food—eating after sunrise and stopping once the sun went down. That pattern gave the body enough time to rest without compromising nutrition. Today’s eight-hour windows are much shorter and may lead to overeating at once, which isn’t beneficial.”
Dr Panda stressed that fasting is not a cure-all. “For heart health or weight management, you need more than fasting. You must eat a whole-food diet, move your body, sleep well, manage stress, and above all, stay consistent. Anything extreme, whether in diet, exercise, or lifestyle, can harm the body.”
This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS.
