# The Evidence for and Against Intermittent Fasting

> A 2022 New England Journal of Medicine trial found time-restricted eating produced no more weight loss than ordinary calorie counting when calories were matched. Here is what the evidence on intermittent fasting actually shows.

*Section: Lifestyle — By Priya Anand (Lifestyle & Travel Editor) — Published September 23, 2025, updated July 7, 2026 — 5 min read*

Canonical URL: https://dailyjunction.co.uk/lifestyle/evidence-intermittent-fasting
Tags: intermittent fasting, diet, weight loss, health, nutrition

## Key takeaways

- The most studied forms are 16:8 (eating within an 8-hour window) and 5:2 (restricting calories on 2 days a week)
- A 2022 New England Journal of Medicine trial found no weight-loss advantage over standard calorie restriction when calories were matched
- The 2022 NEJM trial suggests the weight-loss mechanism is reduced calorie intake, not fasting itself
- Intermittent fasting is not suitable for pregnant women, under-18s, or people with a history of eating disorders
- For some people, a 16:8 eating window is simply an easier way to eat less without counting calories

## Context: separating the science from the hype

Intermittent fasting has been one of the most popular diet trends of the past decade, generating best-selling books, celebrity endorsements and sweeping claims about weight loss, longevity and metabolic health. It has also attracted serious scientific study — which makes it an unusually good case for separating genuine evidence from marketing. The honest picture that emerges is more modest, and more useful, than either the hype or the backlash suggests: intermittent fasting is a legitimate tool that works for some people, for reasons less exotic than its promoters claim. Understanding what the evidence actually shows helps you decide whether it's worth trying without falling for the overselling.

## The data: what the trials actually found

Intermittent fasting comes in several forms, the most studied being 16:8 (eating within an 8-hour daily window) and 5:2 (restricting to around 500-600 calories on two non-consecutive days a week). Crucially, it prescribes when to eat, not what — which is part of its appeal for people who dislike counting calories.

The most important piece of evidence is a 2022 study in the New England Journal of Medicine, which directly compared time-restricted eating against standard calorie restriction over a year:

| Comparison in the 2022 NEJM trial | Result |
|---|---|
| Time-restricted eating vs standard calorie restriction | No significant difference in weight loss |
| When calories were matched | Timing conferred no extra benefit |
| Implied mechanism | Weight loss driven by eating less, not timing |

The finding was clear: when total calories were matched, restricting the eating window produced no additional weight loss. This aligns with the broader body of research, which consistently indicates that the weight loss people see on intermittent fasting comes from consuming fewer calories overall — not from the timing of meals or any special fat-burning effect of fasting itself.

## What's changing: a more sober scientific consensus

The early enthusiasm for intermittent fasting rested partly on animal studies and on claims about metabolic and longevity benefits that have not clearly translated to well-controlled human trials. As the research has matured, a more sober consensus has emerged: intermittent fasting is roughly as effective as other calorie-reduction approaches for weight loss — no better, no worse — and the grander claims about unique metabolic or lifespan benefits in humans remain unproven. This is not a debunking so much as a right-sizing: it works, but through the same basic mechanism as any diet that reduces calorie intake, which means the question is not whether it's magic but whether it happens to suit you.

> "The best diet is the one you can actually stick to. For some people, a restricted eating window makes eating less feel effortless. For others it's miserable and backfires. That individual fit matters far more than any claimed metabolic magic — because adherence, not mechanism, is what determines whether any diet works." — a view consistent with how the British Dietetic Association assesses intermittent fasting.

## What it means for you (should you try it?)

The practical takeaway is refreshingly simple. If the idea of eating within a set window — say, skipping breakfast and eating from noon to 8pm — appeals to you and makes it easier to eat less without tracking, intermittent fasting is a perfectly reasonable approach worth trying. If the thought of fasting periods fills you with dread, or if you find you overeat after a fast, it's not for you, and that's fine — there's no evidence you'd be missing out on a unique benefit. The key is to judge it on whether it helps you eat well sustainably, not on the exaggerated promises. And it's genuinely important to know it's not for everyone: it's unsuitable during pregnancy, for under-18s, for anyone with a history of eating disorders, and for people with certain medical conditions or medications. For alternative evidence-based approaches, our guides on [the Mediterranean diet](/lifestyle/mediterranean-diet-uk-guide) and [cheap, healthy meals](/lifestyle/cheap-healthy-meals-uk-2026) cover eating patterns with strong evidence behind them, and better sleep — covered in our piece on [improving sleep quality](/lifestyle/how-to-improve-your-sleep-quality) — also supports healthy weight management.

It's also worth noting a practical downside that gets less attention than the claimed benefits: for some people, long fasting windows lead to poorer food choices, not better ones. Arriving at your first meal ravenous can make it harder to eat moderately and well, and some people find that a compressed eating window pushes them toward quick, calorie-dense foods rather than balanced meals. There's also the social dimension — eating windows that don't align with family meals, work schedules or social occasions can make fasting hard to sustain and, for some, isolating. None of this makes intermittent fasting bad; it simply reinforces the central finding that fit matters more than mechanism. If a pattern of eating leaves you eating better and feeling good, it's working; if it leaves you preoccupied with food, overeating later, or dreading mealtimes, it isn't, regardless of what the trend promises. That honest, individual test is far more useful than any universal claim about the method.

## What to watch next

Watch for continued research into whether intermittent fasting has benefits beyond weight loss — some studies explore effects on blood sugar control and other markers, but the evidence remains preliminary and shouldn't be oversold. Be especially sceptical of the large and lucrative market of intermittent-fasting apps, supplements and programmes making bold claims the science doesn't support, since the honest evidence — that it works about as well as any other calorie-reduction method — doesn't sell as well as promises of metabolic transformation. And remember the broader principle the research keeps confirming: no single dietary pattern is uniquely effective for everyone, and the most reliable predictor of whether any approach works is whether a person can sustain it comfortably over the long term. On that measure, intermittent fasting is one legitimate option among several, best judged by personal fit rather than by hype.

## Frequently asked questions

### What are the main types of intermittent fasting?

The most studied are 16:8 (eating only within an 8-hour daily window, such as noon to 8pm, and fasting the other 16 hours) and 5:2 (eating normally for five days and restricting to around 500-600 calories on two non-consecutive days). Alternate-day fasting is a more extreme version. Intermittent fasting makes no rules about what you eat — only when — which distinguishes it from most diets and is part of its appeal for people who dislike calorie counting or food restrictions.

### Does intermittent fasting actually work better than other diets for weight loss?

The evidence says: not inherently. A 2022 study in the New England Journal of Medicine directly compared time-restricted eating with standard calorie restriction over a year and found no significant difference in weight loss when total calories were matched. Other research points the same way: the weight loss people experience on intermittent fasting appears to come from eating less overall, not from the timing of meals or any special metabolic effect of fasting. It works about as well as continuous calorie restriction — no better, no worse — for most people.

### So is there any point to it?

For some people, yes — as a practical tool rather than a magic mechanism. If restricting your eating to an 8-hour window makes it easier to eat less without tracking calories, that's a genuine benefit, because the best diet is usually the one a person can actually stick to. Some people find skipping breakfast and eating from noon to 8pm effortless; others find fasting periods miserable and end up overeating afterward. It suits some people's preferences and routines and not others, which is the honest bottom line.

### Who should not try intermittent fasting?

Intermittent fasting is not appropriate for pregnant or breastfeeding women, children and adolescents, people with a history of eating disorders (where any form of food restriction can be risky), people with type 1 diabetes or others on medications that require food, and anyone who is underweight. People with type 2 diabetes or other conditions should check with their GP first. Because it involves periods of not eating, it interacts with several health conditions and medications, so it is not a universally safe approach despite its popularity.

## Sources

- [New England Journal of Medicine (2022) — Calorie Restriction with or without Time-Restricted Eating](https://www.nejm.org/doi/full/10.1056/NEJMoa2114833)
- [British Dietetic Association — intermittent fasting and fad diets](https://www.bda.uk.com/resource/intermittent-fasting.html)
- [NHS — weight loss and healthy eating](https://www.nhs.uk/live-well/healthy-weight/)

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