Those hoping to lose weight this year might be tempted to try to a diet challenge in the hopes of kick-starting their weight loss. But while we might think these kinds of short-term, restrictive diets will help give our waistlines a nudge, psychology and physiology shows us why this strategy can be so hard to stick to – and why it probably won’t result in long-term weight loss.
Research estimates that as few as 20% of people who lose weight through dieting manage to keep the weight off long-term.
For decades, psychologists have been trying to understand why it is that diets so often fail.
One potential reason for this is that diets often involve strict food rules – such as avoiding the foods you enjoy.
The problem with this strategy is that the foods people tend to crave most – such as chocolate, ice cream and crisps – activate the brain’s reward system. This creates positive feelings.
When we cut these foods out of our diet, we lose the pleasure they bring. This can then trigger food cravings – a complex psychological process where we experience an intense desire to eat a particular food, even when we’re not hungry.
Food cravings are often dependent on mood and may be particularly bad when we feel stressed. They can also be especially intense in the afternoon and evening when we feel more tired and have less willpower to resist these cravings.
Food cravings can drive overeating, especially when trying to diet. One review even showed that when people deliberately excluded certain foods from their diet, they experienced an increase in cravings for the foods they were avoiding.
Although the review’s authors conclude that this response can be unlearned, it explains why even short-term restrictive diets tend not to work. Crash diets can trigger stronger food cravings, which can make it harder to stick to your goals – and may even lead to weight gain instead.
Repeated dieting failures can also harm self-efficacy (our belief in our own ability to succeed), a psychological resource important for making lasting behaviour changes.
Nutritionists also agree that short-term restrictive diets aren’t great for long-term weight loss success.
Our appetite (how hungry we feel) and satiety (how long we feel full) are controlled by complex physiological signalling pathways that play a significant role in weight loss.
When we follow very low-calorie diets, our bodies react by increasing appetite, reducing satiety and even reducing energy expenditure (how many calories we burn).
The body also compensates for drastic calorie reductions by sending stronger hunger signals to the brain. This can drive overeating.
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These physiological responses mean diets that are too restrictive can make weight loss harder – and may even lead to weight regain.
From an evolutionary perspective, these responses helped our ancestors to survive food scarcity – but today, it explains why severe calorie restriction so often leads to weight regain. In fact, research shows that people tend to regain about 50%–70% of the weight they lose after dieting.
Another possible explanation for this phenomenon is that you’re not just losing fat when the scale drops – you lose muscle too. This matters because muscle is a key contributor to resting energy expenditure, which is part of your metabolism. Research has also shown that a loss of muscle mass is associated with weight regain.
Since rapid weight loss diets create a large energy deficit and may contain lower amounts of protein, this increases the risk of losing muscle mass. It also increases your chances of regaining weight you may have lost while on the diet.
The best strategies for weight loss
If you’re aiming to make a substantial weight loss attempt, an “all-or-nothing” crash diet may not be your best option. A slower, more balanced approach is far more likely to protect your muscles and support longer-lasting results.
Think nutrient quality, not calories
When it comes to eating well, the key is not to “diet”. As we’ve shown, restricting calories often backfires as our bodies and brains compensate by increasing food cravings and hunger signals. So instead of focusing on what to cut out, think about what you can add to meals to make them healthier.
The types of food we eat influences our appetite and satiety signals – not just the number of calories we consume. For example, protein provides feeling of fullness, and high-fibre carbohydrates keep us more satisfied than highly processed refined ones.
So, aim for nutrient-rich foods. Adding plenty of fibre to your meals, such as whole grains, legumes, lentils, beans, fruits and vegetables, is a great start.
Research suggests that eating more fibre as part of a balanced diet can also help you maintain a healthy body weight throughout your life.
So, rather than making short-term changes in January, aim for small swaps you can stick with throughout the year.
Think like a health coach
Health psychologists have developed frameworks of behaviour change techniques that are known to help people change their physical activity and eating behaviour longer term. These evidence-based techniques are usually used by health coaches to support patients with lifestyle changes – but you can be your own coach by applying some of them yourself.
Examples include setting goals, making an action plan, identifying barriers, or teaming up with a friend or partner.
In practice, this could mean setting a goal to lose a realistic amount of weight per week incrementally (around one to two pounds per week), identifying the things that might get in the way of your goals, exercising with a friend and tracking your progress.
Quick-fix, low-calorie diet challenges might promise fast results, but they rarely deliver lasting change. Following evidence-based advice from the fields of psychology and nutrition can help you avoid the restrictive diet trap this January and achieve more sustainable, longer term lifestyle changes.
