Do any diets actually work?

So many diet plans claim to help you slim down, but will any of them actually help you achieve lasting, healthy weight loss?

These days, diets have a bit of a mixed reputation. Sure, there are still a few big hitters holding onto the headlines – paleo, keto, 5:2, the ever-reliable Mediterranean – but with influencers and nutritionists increasingly preaching the gospel of smart, sustainable eating, cayenne pepper and wheatgrass fasts are, mercifully, becoming a thing of the past.

But is there ever a good reason to go on a traditional diet? Which ones are worth considering? And how do you stop yourself from putting the weight back on once you’re finished?  

First, the bad news: for most people, diets don’t work at all, at least over the long term. According to a recent study based on the results of 121 random trials with nearly 22,000 patients, considering 14 different diets, most worked to reduce weight and risk factors for cardiovascular disease over the short term – but in 12 months, the benefits ‘largely disappear.’ 

Another meta-analysis (basically, a review of lots of studies) from 2018, which followed 29 long-term weight loss studies, showed that dieters regained more than half of their lost weight within two years, and more than 80% within five years. 

Dietary downsides

Why does this happen? Well, firstly, it’s important to understand that almost every diet will work, at least for a while, because every diet either cuts the amount of calories you’re taking in, or makes you more mindful about what you’re eating, or both.

If you’re on the paleo diet (which is supposedly based on the diets of cavemen), for instance, your food choices are limited to unrefined carbs such as sweet potatoes, fruit, veg and meat. That means you won’t be eating processed, ‘hyperpalatable' foods that it’s easy to binge on – it’s much easier to eat a packet of Doritos than five heads of broccoli – but also that you’ll be making a conscious decision about everything you put in your mouth.

With calorie-counting diets, this effect is even more pronounced – you might be able to eat sugary snacks, but it’s impossible to overeat if you stick to the plan. More extreme, less science-based diets will seem even more miraculous over the short term, as cutting carbs and salt can cause your body to rapidly drop water weight – but these effects won’t last. 

As for why more sensible diet options stop working, explanations vary. Most obviously, willpower fades: it’s (relatively) easy to avoid eating carbs, cake or anything beige for a couple of weeks, but much tougher to stay strong over a season of birthdays, weddings and work parties. You might also have heard that dieting for an extended period can slow your metabolism – causing your body to burn (and need) fewer calories – but here, things get slightly more complicated.

Cutting back

It’s true, for instance, that ‘eat less, move more’ is usually good fat loss advice – if you burn more calories than you take in, you’ll definitely lose weight. But our metabolisms evolved to keep us functioning when food was scarce, so when you start to eat less your body cuts back on energy expenditure, lowering your resting metabolic rate and even the calories you burn through exercise.

By cutting calories you might also increase your body’s hunger signals, giving you cravings to eat more at the same time as your body cuts back. How much difference this makes varies from person to person – but it also changes as you get leaner, so what works when you’re packing a bit of extra timber might no longer work as your abs start to emerge.

So does this mean that diets are useless? Well, not necessarily. As mentioned above, diets make you more mindful about what you eat, but they might also help to reset unhealthy eating habits by changing your attitude to snacking or helping you to adopt new habits.

Switch from cereal to scrambled eggs in the morning, for instance, and you don’t need to be on a keto plan to make the change permanent – giving you an early-morning hit of filling protein and cutting back on sugar.

Learn to make a couple of tasty recipes including green veg, and you’re less likely to call for a Deliveroo when hunger hits. Over the long term, sustainability is key to keeping in shape, so if you’re going to diet, it makes sense to choose an option that’s broadly sustainable, even if you ‘cheat’ on it occasionally – think paleo or Mediterranean, rather than extreme fasting or (unless you’re really committed) keto.

Remember: good eating is for life, not just for your summer holidays.