We Were Wrong About Restrictive Diets, Decades of Research Says

Those looking to achieve weight loss this year are often drawn to a diet challenge as a way to spark fast progress.

Yet although short, strict plans can feel like they should “jump-start” a slimmer waist, both psychology and physiology help explain why this approach is difficult to maintain - and why it is unlikely to produce long-term weight loss.

Studies suggest that only around 20 per cent of people who lose weight through dieting manage to keep it off in the long term. For many decades, psychologists have tried to pin down why diets so frequently fail.

Why restrictive dieting so often backfires

One key issue is that many diets rely on rigid food rules - for example, banning foods you genuinely like.

The snag is that commonly craved items (such as chocolate, ice cream and crisps) stimulate the brain’s reward system, which generates pleasant feelings. When these foods are removed, people lose that enjoyment, and this can set off food cravings - a complex psychological process marked by a powerful urge to eat a specific food even when you are not physically hungry.

Food cravings are often tied to mood and can be worse during periods of stress. They may also peak in the afternoon and evening, when fatigue is higher and willpower is often lower.

These cravings can contribute to overeating, particularly when someone is trying to diet. One review found that when people intentionally cut out particular foods, cravings for the very foods they were avoiding tended to increase.

Although the authors of that review suggest this reaction can be “unlearned”, it helps to explain why even short-term restrictive plans frequently fall apart. Crash diets may intensify cravings, making targets harder to stick to - and in some cases contributing to weight gain rather than loss.

Repeated attempts that do not work can also undermine self-efficacy (your belief in your own ability to succeed), which is an important psychological resource for sustaining behaviour change.

The physiology: appetite, satiety and energy expenditure

Nutritionists also tend to agree that short-term restrictive dieting is a poor route to lasting success.

Your appetite (how hungry you feel) and satiety (how long you feel satisfied after eating) are regulated by complex physiological signalling pathways, and these systems strongly influence weight loss outcomes.

When people follow very low-calorie plans, the body often responds by increasing appetite, reducing satiety, and lowering energy expenditure (the number of calories you burn). In addition, the body may compensate for sharp calorie cuts by sending stronger hunger signals to the brain, which can encourage overeating.

Together, these physiological reactions mean that diets that are too restrictive can make losing weight more difficult - and can increase the likelihood of regaining it.

From an evolutionary standpoint, these responses helped our ancestors survive when food was scarce. In today’s environment, however, this is one reason severe calorie restriction so often ends with weight regain. Research indicates that people commonly regain about 50–70 per cent of the weight they lose after dieting.

Muscle loss, metabolism and regain

Another factor is that the number on the scales can drop not only because of fat loss, but also because of muscle loss. This matters because muscle is a major contributor to resting energy expenditure, which is part of your metabolism. Research also links reduced muscle mass with subsequent weight regain.

Because rapid weight loss diets typically create a large energy deficit and may provide less protein, they can raise the risk of losing muscle - and, as a result, increase the chances of regaining weight lost during the diet.

The best strategies for weight loss

If you want to make a meaningful weight loss attempt, an “all-or-nothing” crash diet is unlikely to be the best choice. A steadier, more balanced approach is more likely to preserve muscle and support results that last.

Think nutrient quality, not calories

When the goal is healthier eating, the most helpful mindset is often not to “diet” at all. As outlined above, calorie restriction can backfire when the brain and body respond with stronger cravings and hunger signals. Instead of obsessing over what to eliminate, consider what you can add to meals to improve them.

Importantly, appetite and satiety are influenced by the types of foods you choose - not only by total calories. For instance, protein tends to improve fullness, and high-fiber carbohydrates often keep people more satisfied than highly processed, refined options.

Aim to prioritise nutrient-rich foods. A good starting point is boosting fiber by including whole grains, legumes, lentils, beans, fruits and vegetables.

Research suggests that higher fiber intake as part of a balanced diet may also help people maintain a healthy body weight across the lifespan. So rather than making dramatic, short-lived changes in January, focus on small swaps you can realistically keep up all year.

Think like a health coach: behaviour change techniques for weight loss

Health psychologists have developed frameworks of behaviour change techniques shown to help people improve physical activity and eating habits over the longer term. These evidence-based tools are often used by health coach professionals to guide lifestyle change - but you can apply many of the same approaches yourself.

Useful examples include setting goals, building an action plan, anticipating barriers, and partnering with a friend.

In practical terms, this might involve setting an achievable weekly target (around 0.5–1 kg per week), working out what could derail your plan, exercising with a friend, and monitoring your progress over time.

Add resistance training to support muscle and resting energy expenditure

Because muscle supports resting energy expenditure, preserving it matters when you are trying to lose weight. Including resistance training (such as weights, resistance bands or bodyweight exercises) alongside a balanced diet can help protect muscle during weight loss and may reduce the risk of regain linked to muscle loss.

Pay attention to stress and sleep to reduce food cravings

As food cravings can worsen when stress is high and willpower is low, strategies that improve sleep and reduce stress can indirectly support eating goals. Regular sleep routines and stress-management habits (for example, walking, relaxation techniques or structured downtime) may make it easier to navigate afternoon and evening craving peaks.

Quick-fix, low-calorie diet challenge plans can promise rapid change, but they rarely deliver lasting results. Using evidence-based guidance from psychology and nutrition can help you avoid the restrictive diet trap this January and make more sustainable, long-term lifestyle changes.

Chloe Casey, Lecturer in Nutrition and Behaviour, Bournemouth University and Sarah Hillier, Senior Lecturer in Nutrition, Bournemouth University

This article is republished from The Conversation under a Creative Commons licence. Read the original article.