Best diet for weight loss: which diet really works?

What is the best diet for weight loss?

The best diet for weight loss is a way of eating you enjoy enough to keep for years, built on whole foods, with enough protein and fibre and few ultra-processed foods and sugary drinks. Which named diet you follow matters much less than most books and adverts suggest.

That answer can feel disappointing if you hoped for one clear winner. But it is also good news. It means you do not have to force yourself into a style of eating that does not suit you, your family or your culture.

If you love bread, pasta and fruit, a Mediterranean or lower-fat pattern can work well. If you feel less hungry with fewer starchy foods, a sensible lower-carb pattern can work too. Both can lead to real weight loss when the food is good and the portions fit your body.

On this page we compare eight popular approaches, explain what the strongest studies show, and help you choose. Please talk to your doctor first before you change the way you eat, especially if you have a health condition or take medicines.

What head-to-head diet trials show

Head-to-head trials show that diets with very different mixes of fat, carbohydrate and protein lead to similar average weight loss over one to two years. This finding has been repeated in many trials and in large reviews that pool them.

Lower-fat versus lower-carb: DIETFITS

In the DIETFITS trial at Stanford, more than 600 adults with a higher weight were randomly assigned to a healthy low-fat or a healthy low-carbohydrate diet for twelve months. Both groups were coached to eat good-quality food, not just to cut a nutrient.

After a year, the low-fat group had lost 5.3 kg on average and the low-carb group 6.0 kg. The gap was small and could have been due to chance.

The researchers also tested whether genes or insulin levels could predict who would do better on which diet. They could not.

Four diets, two years: POUNDS Lost

The POUNDS Lost trial followed 811 adults on four reduced-calorie diets that differed in fat (20 or 40 % of energy), protein (15 or 25 %) and carbohydrate (35 to 65 %). All four used similar, heart-healthy foods.

At six months, people in every group had lost about 6 kg, around 7 % of their starting weight. After a year, weight slowly crept back in all groups. At two years, the differences between diets were tiny and not significant.

One thing did stand out: people who came to more group sessions lost more weight, about 0.2 kg for every session attended. Support and staying engaged mattered more than the recipe.

What the big reviews add

A network meta-analysis in the BMJ combined 121 trials with almost 22,000 adults and 14 named diets. At six months, low-carb and low-fat diets produced similar weight loss compared with usual eating, about 4.5 kg. By twelve months, the effect had shrunk for every diet.

A Cochrane review of 61 trials came to the same conclusion for carbohydrates. Low-carb and balanced-carb weight-reducing diets probably lead to little or no difference in weight after one to two years, in people with and without type 2 diabetes. The average gap was about one kilo or less.

So the evidence is consistent. Any of the well-known diets can help, as long as it lowers the energy you eat, keeps quality high and fits your life well enough to continue.

Why do different diets give similar results?

Different diets give similar results because they all work by helping you eat a little less energy than you use, and because most people find it hard to keep any strict plan going for long. The labels differ; the underlying mechanism is largely the same.

A low-carb plan cuts bread, rice and sweets, while a low-fat plan cuts butter, fried food and fatty snacks. A Mediterranean plan swaps processed food for vegetables, pulses and fish. Each route removes some energy-dense foods from your day.

Your body also pushes back: when you lose weight, hunger hormones change and your body uses a little less energy. This is biology, not weakness, and it is the same whatever diet you choose. Our page on genetics and biology explains why.

That is why keeping it up is so important. In the trials, the people who did best were those who stayed with their plan, kept coming to support sessions and kept adjusting. The best predictor of success was not the diet name but daily habits that lasted.

The world around you plays a part too. Cheap, heavily marketed snacks and drinks make any diet harder. Read more about the food environment and how to protect yourself from it at home.

Weight loss diets compared: the evidence at a glance

Each popular weight loss diet has strengths and weak spots, and some need medical advice for certain people. The table gives a quick overview; the sections below explain the details.

The table is a general overview, not personal advice. Your doctor or a dietitian can help you weigh these points against your own health.

Is the Mediterranean diet good for weight loss?

The Mediterranean diet works for weight loss as well as other diets do, and it has one of the strongest records for heart health. It is a pattern of eating rather than a set of strict rules, which makes it easier to keep up.

A typical Mediterranean plate has plenty of vegetables, beans or lentils, whole grains, a handful of nuts, olive oil as the main fat, fish a few times a week, and fruit for dessert. Red meat, processed meat, sweets and sugary drinks are kept for now and then.

In the Spanish PREDIMED-Plus trial, 626 people aged 55 to 75 with metabolic syndrome followed either a reduced-calorie Mediterranean diet with more physical activity and support, or usual care. After one year, the first group had lost 3.2 kg on average against 0.7 kg in the comparison group.

A third of the Mediterranean group lost at least 5 % of their body weight, compared with about one in eight in the other group. Waist size, blood sugar and blood fats also improved. Note that the diet was combined with walking and support, which is exactly the mix we recommend.

The BMJ review found that when effects on heart risk faded after a year for most diets, the Mediterranean pattern was the exception. That makes it a good default choice if you have no strong preference.

Making it work in any kitchen

• You do not need Mediterranean ingredients. The principle is vegetables, pulses and whole grains first, in the dishes of your own culture.
• Olive oil is healthy but rich in energy. Measure it with a spoon instead of pouring from the bottle.
• Tinned fish, frozen vegetables and dried lentils keep costs down.
• Nuts are a good snack in a small handful, not a whole bag.

Our guide to the best nuts for weight loss shows how much olive oil, nuts and avocado fit a weight-loss diet.

Low-carb and keto for weight loss

Low-carb and keto diets can help people lose weight, but over one to two years they do not lead to clearly more weight loss than balanced diets. They suit some people well and others not at all.

There is no single definition of low-carb. The American Diabetes Association describes a low-carbohydrate pattern as getting about 26 to 45 % of energy from carbohydrates. A very low-carb or keto plan usually aims for about 20 to 50 g of carbohydrate a day, low enough for the body to make ketones.

What the evidence shows

The Cochrane review found that low-carb weight-reducing diets probably make little or no difference to weight compared with balanced-carb diets, both in the first months and after one to two years. That was true both with and without type 2 diabetes.

Keto diets often give fast early results on the scale. Part of that early drop is water, released when the body uses up its stored carbohydrate. Over a year, the gap with other diets becomes small.

The BMJ analysis also noted that low-carb diets lowered LDL (“bad”) cholesterol less than low-fat diets did. If your cholesterol is high, ask your doctor to check it after a few months.

Keto and very low-carb: check with your doctor first if…

• you use insulin or other diabetes medicines. Blood sugar can drop quickly when you cut carbs, and doses may need to be lowered from the first day. The American Diabetes Association advises starting very low-carb eating only with a knowledgeable health professional.
• you take an SGLT2 inhibitor (diabetes or heart medicines whose names end in “-gliflozin”). Combined with keto, they have caused a dangerous acid build-up in the blood called ketoacidosis, sometimes with near-normal blood sugar.
• you have kidney disease, are pregnant or breastfeeding, or have had an eating disorder. Very low-carb eating has not been studied enough to call it safe in these situations.
• you take medicines for blood pressure or water tablets. Very low-carb eating makes you lose fluid at first, which can cause dizziness.

Never stop or change your medicines on your own. Bring this list to your appointment, or use our doctor visit checklist to prepare.

If you choose lower-carb, do it well

A healthy low-carb plate is mostly vegetables, with fish, eggs, poultry, tofu, pulses or dairy, and some nuts or olive oil. It is not a plate of bacon, sausages and cheese.

Keep non-starchy vegetables high and include some pulses or berries to protect your fibre intake. A moderate lower-carb pattern is often easier to keep for years than strict keto.

Low-fat, DASH and plant-based diets

Low-fat, DASH and plant-based diets are all good options for weight loss when they are built on whole foods. They tend to be high in fibre and bulk, which helps many people feel full on fewer calories.

Low-fat

A low-fat diet cuts back on butter, cream, fatty meat, pastries and fried food. In DIETFITS it worked as well as low-carb, as long as people chose good-quality foods. The weak spot is processed “low-fat” products: check the label, because some contain a lot of added sugar.

DASH

DASH stands for Dietary Approaches to Stop Hypertension. It was designed to lower blood pressure, with plenty of vegetables, fruit, whole grains, low-fat dairy, beans and nuts, and less salt, red meat and sugar.

A review of trials found that people following DASH lost about 1.4 kg more than people on comparison diets over 8 to 24 weeks, with a bigger effect in people with a higher weight. If you have high blood pressure, DASH is a natural place to start.

Plant-based and vegetarian

A review of twelve randomised trials with more than 1,100 people found that those on vegetarian diets lost about 2 kg more than those on non-vegetarian diets, over a median of about four months. Vegan diets gave slightly more weight loss than diets that still included eggs and dairy.

Pulses, whole grains and vegetables are cheap in many countries, which helps. Plan your protein at every meal, and if you eat no animal foods at all, make sure you get vitamin B12 from fortified foods or a supplement.

High-protein diets and meal replacements

A higher-protein diet may help some people feel fuller, but in long trials it did not lead to much more weight loss than a normal-protein diet. Meal replacements can help when combined with support, while very low-calorie liquid plans are a medical treatment, not a self-help diet.

High-protein

In POUNDS Lost, people on 25 % protein lost 3.6 kg after two years, and those on 15 % protein lost 3.0 kg: a difference too small to matter.

Shorter trials are a little more positive. A review of 24 studies found that higher-protein, reduced-calorie diets led to slightly more fat loss and helped protect lean tissue such as muscle, and several of those studies reported people felt fuller.

So protein at each meal is a sensible habit within any diet, especially together with strength exercise.

Choose varied sources such as pulses, fish, eggs, dairy, poultry and tofu, rather than lots of processed meat. If you have kidney disease, ask your doctor or dietitian how much protein is right for you before raising it.

Meal replacements

Meal replacements are shakes, soups or bars with a fixed amount of energy and added vitamins and minerals. A systematic review found that programmes using them led to more weight loss after a year than programmes without them, especially when people also had regular support.

They take away daily decisions, which some people find helpful at the start. The challenge comes when ordinary meals return: you still need to learn which everyday foods and portions keep you on track.

Very low-calorie liquid plans: medical supervision only

A total diet replacement swaps all food for formula products for a while, at a very low energy intake.

In the DiRECT trial, people diagnosed with type 2 diabetes in the previous six years, and not using insulin, used about 825 to 853 kcal a day of formula for three to five months, inside a structured programme run by health professionals.

They lost 10 kg on average, and almost half were in diabetes remission after a year, compared with 4 % in the usual-care group. But their diabetes and blood pressure medicines were stopped and monitored by their doctors, and food was carefully reintroduced afterwards.

Very low-calorie diets are not advice from us and are not something to try on your own. They are only safe under medical supervision, because medicines often need changing and side effects need checking. If you are interested, talk to your doctor about whether a supervised programme exists where you live.

What every good weight loss diet has in common

Every weight loss diet that works in trials shares a few features: it lowers energy intake, keeps food quality high and is realistic enough to follow. You can use these points to judge any plan, including ones not on this page.

Enough protein

Protein foods such as pulses, fish, eggs, yoghurt, poultry and tofu help you feel full. Spreading them across your meals is easier than one large portion at dinner. Our macro calculator gives a rough idea of how much protein suits your height.

Plenty of fibre

Fibre comes from vegetables, fruit, pulses, whole grains, nuts and seeds. These foods add bulk to a meal for relatively little energy, which is one reason vegetarian, DASH and Mediterranean patterns perform well.

The American Diabetes Association encourages people to eat at least the amount of fibre recommended for the general public, preferably from food. Adding a portion of beans, an extra vegetable or switching to whole grain bread are easy first steps.

Few ultra-processed foods

Ultra-processed foods are industrial products such as crisps, sweets, packaged cakes, sugary cereals and many ready meals. In a small controlled study of 20 adults at the US National Institutes of Health, volunteers given an ultra-processed menu chose to eat around 500 kcal a day more than on a menu of unprocessed food. They gained weight within two weeks.

The American Diabetes Association gives the same practical advice for every eating pattern: lots of non-starchy vegetables, few added sugars and refined grains, and whole foods over highly processed ones where you can.

Few sugary drinks

A BMJ review of trials and cohort studies found that free sugars and sugar-sweetened drinks are a real driver of body weight, mainly because they add extra energy to the day. Water, unsweetened tea and coffee, and sparkling water are the simplest swaps of all.

Realistic and enjoyable

A plan that bans your favourite foods forever, or that you cannot afford or cook, will not last. Room for a treat now and then is not a weakness of a diet; it is often what keeps it going.

How do you choose the right diet for you?

To choose your diet, start with your health, then your food preferences, then your daily routine. The style that passes all three checks is the best one for you, whatever its name.

Step 1: check your health first

Before you start any weight loss diet, see your doctor if you have diabetes, kidney disease, heart disease, high blood pressure, are pregnant, take several medicines or have had an eating disorder. Ask which styles are safe and whether any medicine needs to be adjusted.

Step 2: look at what you already enjoy

Write down the meals you eat most often and the ones you love. A diet that keeps most of your favourite dishes, slightly changed, is far easier than one that replaces them all.

Step 3: be honest about your life

Think about your budget, how much time you have to cook, who you eat with, shifts or travel, and your culture or religion. The plan has to work on a tired Tuesday, not only on a calm Sunday.

Step 4: match your situation to a style

Step 5: test it for four weeks

Try your chosen style for about a month. Then ask yourself: Am I hungry most of the time? Do I dread meals? Can my family eat this too? Could I imagine eating like this a year from now?

If the answers are mostly good, keep going and fine-tune. If not, change the style, not your goal. Switching to a plan that suits you better is a smart move, not a failure.

Some people also like to change when they eat, not only what. That is a separate approach with its own pros and cons, explained on our page about intermittent fasting.

Red flags: diets to skip

Skip any diet that promises very fast weight loss, bans whole food groups without a medical reason, or depends on special products, pills or detox teas. These plans may give a quick drop on the scale but are rarely safe or lasting.

• Promises of many kilos in a week or two. Much of a very fast early drop is water. A steady pace is safer; see our page on safe weight loss.
• One “magic” food or drink, such as soups, juices or vinegar, eaten at every meal.
• Very low intake without a doctor. In supervised programmes, medicines are checked and changed first, and food is brought back step by step; doing it alone skips those safety steps.
• Expensive products you must keep buying, with no plan for normal meals.
• Rules that make you feel guilty or anxious about food. If dieting has led to bingeing or a troubled relationship with food, our page on emotional eating and psychological support can help.

Making your diet last: the first 12 weeks

A diet lasts when you change a few habits at a time, track them kindly and adjust as you go. The first three months are when most people either build routines or give up, so plan them on purpose.

Weeks 1 to 4: small swaps

• Pick two or three changes only, for example water instead of sugary drinks, vegetables at lunch and dinner, and protein at breakfast.
• Keep the foods that fit your chosen style visible and easy to reach.
• Write down what you eat for a few days, without judging, to see where the easy wins are.

Weeks 5 to 8: routines

• Plan your dinners a few days ahead and shop with a list.
• Find three quick meals you can make on busy days.
• Add a daily walk, even a short one, to support your energy and mood.

Weeks 9 to 12: review and adjust

• Look back: which changes feel natural now, and which still feel like a fight?
• Keep what works and replace what does not.
• If your weight stalls, check portions, drinks and weekend eating before you blame the diet.

Weight loss slows over time for everyone, whatever they eat. Planning for that phase makes regain less likely; our page on weight regain explains what helps.

Diet works best with movement and walking

Diet does most of the work for weight loss, but movement and walking make the result healthier and easier to keep. In PREDIMED-Plus, the Mediterranean diet was combined with more physical activity and support for exactly that reason.

Walking is the easiest place to start, and our guide to walking for weight loss shows how to build it up step by step. If you want more, our free workouts start at Level Start, with seated options and no jumping, and help you keep muscle while you lose weight.

Sleep and stress matter as well. Short nights and constant pressure can make cravings stronger whatever diet you follow. For the full picture, read how to lose weight step by step.

How our free eating plan fits your chosen diet

Obesity Foundation’s free eating plan is practical and flexible, without crash diets or extreme calorie counting, and can be adapted to your tastes and culture. We do not sell diets, shakes or products; we help people lose weight with good food, suitable exercise and walking.

Whichever style appeals to you, such as Mediterranean, vegetarian or a moderate lower-carb pattern, you can adapt our free eating plan to it by swapping foods while keeping plenty of vegetables, protein and whole foods. If you take diabetes medicines, check lower-carb changes with your doctor first.

Not sure yet? Start with the plan as it is and adjust later. Our sample eating plan shows what a full week looks like.

• Get your free eating plan: practical, flexible meals you can adapt to your taste and culture.
• Get the free workout videos: three levels, starting gently with Level Start.
• Book a free video meeting (in English) to talk through your questions about choosing a way of eating.
• Join the free Obesity Foundation Club for tips, encouragement and a place to track your progress.

We are not doctors, and this page cannot tell you which diet is safe for you. Please talk to your own doctor first before you change the way you eat, especially if you have diabetes, kidney disease or take medicines. To learn more about the condition itself, read what obesity is and the treatment options available.