Is intermittent fasting the best way to lose weight?

Last Updated : 03 July 2025

Key takeaways

• Regardless of the diet chosen, creating a calorie deficit is essential to weight loss. Intermittent fasting can be used as a tool to create a calorie deficit.
• Intermittent fasting can be effective for weight loss if you eat fewer calories than you use. The positive health effects are related to weight loss. It’s not known what the long-term effects on health are.
• The problem with intermittent fasting as a way to create a calorie deficit is that it doesn’t necessarily change the nutritional quality of your diet – you can still eat energy-dense nutrient poor foods, which are linked to negative health effects.
• Intermittent fasting can be effective for some individuals; however, it may pose challenges and risks that other dietary approaches might not. Choosing a dietary strategy based on personal health goals, lifestyle, and preferences is more likely to stick.
• Intermittent fasting can lead to disordered eating patterns, nutrient deficiencies, and various adverse effects like dehydration, weakness, and fatigue.

Intermittent fasting is one of the most popular nutrition trends in recent years. People who follow this dietary strategy alternate between periods of eating and fasting. The appeal is easy to understand: rather than focusing on what you eat, it emphasizes when you eat. There are different ways to intermittent fast, but common approaches include the 16:8 method (16 hours of fasting and 8 hours of eating), the 5:2 method (eating normally for five days and restricting calories for two days), and the eat-stop-eat method (24-hour fasts once or twice a week). Intermittent fasting offers structure that many people find helpful. But is this diet a new revolutionary way to lose weight and improve health? We’ll start with the facts, then look at the myth, and finally explain why the myth doesn’t hold up.

Fact: weight loss comes from creating a calorie deficit – and many different approaches can work, not just intermittent fasting.

At its core, weight gain and weight loss is primarily driven by an imbalance between how much energy you eat (e.g., kcal) and how much energy you burn (e.g., through exercise). When someone eats less calories than their body uses for energy, this deficit forces the body to draw on its energy reserves, typically stored at fat. Whether someone achieves this deficit by fasting, reducing portion sizes, increasing physical activity, or changing the types of foods they eat, the underlying principle is largely the same.¹

Intermittent fasting can be one way to create a calorie deficit. By shortening the eating window, some people naturally eat less – especially if they cut out snacking or late-night meals.

Myth: intermittent fasting is a magic bullet for weight loss.

Supporters of intermittent fasting highlight its weight-loss benefits, and for some, it does lead to meaningful results. But when researchers have compared intermittent fasting to more traditional calorie-restricted diets (without a focus on meal timing), findings suggest that it’s not necessarily superior. In other words, weight loss has indeed been seen on the intermittent fasting diet; however, this effectiveness is largely attributed to the calorie deficit it creates.

For instance, a recent systematic review and meta-analysis examined several forms of intermittent fasting, including 16:8, alternate-day fasting, and 5:2, and compared it to a calorie-restricted diet. The study found comparable outcomes in terms of weight loss, insulin sensitivity, and various blood lipids in all diets.^2,3 A similar pattern was seen in other studies, except for a more noticeable reduction in waist circumference with intermittent fasting.⁴ These results suggest that intermittent fasting can be as effective, but not inherently more effective, than other dietary strategies for weight loss. However, another recent systematic review and meta-analysis suggest that while intermittent fasting might reduce weight compared to unrestricted eating, the changes are often minor and may not lead to measurable health improvements over the short term.⁵

That said, there’s growing interest in a specific version of intermittent fasting called early time-restricted feeding – where food intake ends earlier in the day, typically before 3 p.m. A study where eight men with pre-diabetes restricted food to a six-hour eating window and ended food intake before 15:00 found that it improved insulin sensitivity, beta-cell responsiveness (the cells within the pancreas that are responsible for releasing insulin), blood pressure, oxidative stress, and reduced appetite, compared to eating all their food over 12 hours. These improvements occurred regardless of weight loss, indicating that the benefits were independent of changes in body weight.⁶ Researchers speculate that aligning eating patterns with our body’s natural circadian rhythms may play a role.

While these early findings are exciting, it’s important to treat them as emerging science. We still need more long-term evidence in larger and more diverse study groups to confirm the long-term benefits and recommended early time-restricted feeding as an effective dietary strategy for the general population.

Even though intermittent fasting can be effective for some, it may not suit everyone’s biology, lifestyle, or relationship with food. Some people may experience side effects from fasting such as dehydration, too low blood sugar levels, fatigue, weakness, dizziness, too low blood pressure levels, insomnia, nausea, headache or migraines, fainting, indigestion, malnutrition, and excessive hunger while following an intermittent fasting diet.⁷ For others, intermittent fasting can interfere with eating in social settings or lead to feelings of isolation. For people who have a history of disordered eating, the rigid structure of fasting periods can sometimes trigger unhealthy behaviours like bingeing during eating windows or becoming preoccupied with food and hunger.⁸ Intermittent fasting may also not be safe for people with diabetes, children, elderly, or those who are pregnant, underweight, or very physically active.

It’s also worth noting that intermittent fasting doesn’t inherently promote nutritious eating patterns and nutrient deficiencies can occur. Some people may end up eating calorie-dense, low-nutrient foods during their eating windows, which can undermine overall health goals even if a calorie deficit is achieved.

Fallacy: why timing of meals isn’t everything.

One of the appeals of intermittent fasting is that it doesn’t require you to give up specific foods. But this strength can also become a weakness. Focusing exclusively on when to eat can make it easy to overlook what you eat.

Some people assume that fasting allows them to eat whatever they want during the eating window. But the body still responds to overall energy and nutrient intake, regardless of timing. Overeating high-calorie foods or neglecting a healthy diet rich in fruits, vegetables, whole grains, and legumes can lead to nutritional gaps, even on a fasting diet. It's important to eat a balanced and nutritious diet within the eating windows.

Another common pitfall in how intermittent fasting is presented online is what researchers call selection bias: most success stories shared online come from people for whom intermittent fasting worked. It’s not that intermittent fasting doesn’t work – it can! But hearing mostly from success stories creates the illusion that it works for everyone. You rarely hear from the many people who tried it, struggled, and gave up – or who managed to lose weight with other dietary approaches. This can create a skewed perception, leading others to believe that intermittent fasting is universally effective.

Many people may struggle with intermittent fasting, not achieve the desired weight loss, or find it challenging to adhere to the regimen over time. In fact, studies have shown that intermittent fasting is often effective in the beginning, usually within the first 1-6 months; however, many people hit a point where they stop losing weight. This can happen because the body gets used to the new eating pattern, or because people find it hard to stick to the diet over time.⁹ Studies show long-term weight loss is most strongly predicted by whether someone can incorporate the approach to their lives.¹⁰

This highlights why it’s important to look beyond personal anecdotes and understand how different strategies work – or don’t work – for different people. If you’re considering trying an intermittent fasting diet, approach it with a balanced perspective and recognise both its potential benefits and limitations. Also, consider alternative dietary strategies and choose an approach that best aligns with your personal health goals, lifestyle, and preferences.