Intermittent fasting shown to be effective for weight loss in new large-scale study

Key Takeaways:

• A comprehensive analysis of 99 clinical trials found alternate-day fasting to be the most effective form of intermittent fasting for weight loss and improving key health markers.
• Participants practising alternate-day fasting lost an average of 1.3 kg more than those following standard calorie-restricted diets, alongside improvements in waist size, cholesterol, and inflammation.
• However, the differences fell below the threshold considered clinically meaningful for people living with obesity, highlighting the need for longer studies to assess long-term impacts.
  

Intermittent fasting gains further attention as a weight-loss approach

Intermittent fasting has become an increasingly popular method for managing weight, with growing evidence suggesting it may rival or even outperform traditional calorie-reduction diets in some respects. This dietary pattern restricts the window during which food is consumed each day, prompting the body to draw on fat reserves for energy once its immediate glucose supply is depleted.

Prominent institutions such as Johns Hopkins Medicine have long acknowledged the potential health benefits of intermittent fasting, which may extend beyond weight control to broader metabolic health.

Obesity’s continuing burden on public health

Obesity remains a critical public health challenge, affecting approximately two in five adults in the United States. It imposes an estimated annual cost of $173 billion on the American healthcare system. Carrying excess body weight is well established as a major risk factor for chronic diseases, including cardiovascular disease and type 2 diabetes.

Against this backdrop, researchers continue to explore diverse dietary strategies that might help reduce obesity prevalence and mitigate its health impacts.

Large-scale study identifies alternate-day fasting as particularly beneficial

In a recent high-quality analysis published in The BMJ, researchers from the Harvard T.H. Chan School of Public Health, working alongside colleagues from international institutions, sought to evaluate the effectiveness of different intermittent fasting methods. Their investigation pooled data from more than 6,500 adults enrolled in 99 clinical trials worldwide. Most participants were living with obesity and had additional health conditions.

Their findings pointed to alternate-day fasting — a regime where individuals eat normally one day and completely abstain from caloric intake the next — as the most effective intermittent fasting strategy compared to both standard calorie restriction and other time-restricted eating patterns.

As the Harvard team summarised:

“Among all intermittent fasting methods studied, alternate-day fasting – where a person eats normally one day and completely abstains from food the next – was shown to be the most effective.”

Measurable improvements in weight and cardiovascular risk factors

Participants who adopted alternate-day fasting achieved greater weight reduction, losing on average 2.8 pounds (approximately 1.3 kg) more than those adhering to traditional calorie-controlled diets. Beyond weight loss, this approach was linked with notable improvements in several key markers associated with cardiovascular disease and type 2 diabetes risk.

These included significant reductions in waist circumference, total cholesterol, low-density lipoprotein (LDL or “bad”) cholesterol, triglycerides, and C-reactive protein — a marker of systemic inflammation. Collectively, these changes suggest potential benefits for heart health and metabolic disease prevention.

Caution warranted: differences below clinical thresholds

Despite these encouraging outcomes, the researchers highlighted that the differences in weight loss did not meet the commonly accepted threshold of clinical significance, typically defined as a minimum of 4.4 pounds (2 kg) in individuals with obesity. This means that while alternate-day fasting demonstrated statistically meaningful results, the average benefits may not translate into substantial clinical improvements without further supportive evidence.

Zhila Semnani-Azad, who led the study, underscored the need for a cautious and personalised approach:

“Intermittent fasting, despite its promising results, may not be suitable for everyone. Before making significant dietary changes, it is essential to consult healthcare professionals and consider personal medical history, lifestyle, social circumstances, and potential for sustained adherence.”

Looking ahead: need for longer trials

The researchers called for extended studies to explore whether intermittent fasting — and alternate-day fasting in particular — can deliver lasting weight management and cardiovascular benefits over time. Such evidence would be crucial to inform clinical guidelines and support people living with obesity in choosing the most appropriate dietary strategies.

This new analysis offers valuable insights into how intermittent fasting might contribute to tackling obesity and its related health risks, while reinforcing the importance of individualised medical advice and long-term research.

CCH Insight:

There are undoubted benefits to be gained from intermittent fasting, including weight loss. However, the practicalities of some of these diets, such as alternate day fasting, may be very challenging for people living with obesity. Eating next to nothing one day and then normal meals the next can be difficult, especially for people who have cravings or experience ‘food noise’, for example. Time- restricted eating, where the same eating pattern is adhered to every day, may therefore be a more practical form of intermittent fasting for people with obesity, rather than alternate day fasting.