The first time my brother Sam tried to exercise his way out of obesity, he lasted nine days. He was 118 kilograms, he had bought running shoes, and he had downloaded a couch to 5K app designed, as far as he could tell, for people who weighed 70. On day nine his knee swelled up, he felt humiliated in front of the neighbours, and the shoes went in the cupboard for three years. The first time he tried to diet his way out, he lasted six weeks on 1,200 calories, lost eight kilograms, regained eleven, and concluded that he was the problem.
He was not the problem. The plans were. Most obesity diet and exercise advice is written for people who are slightly overweight and already fit, and it is quietly dangerous for people carrying 30 or 40 extra kilograms: too fast, too hard on the joints, too hungry, and too indifferent to the biology that makes big people regain. This is the plan he eventually followed, built with a dietitian and a physiotherapist and checked against the trials. It covers what to eat when you have a lot to lose, how to move when your knees and your confidence are not ready for a gym, how fast to lose, and how to keep it off, which is the part almost everyone skips. No shame, sources throughout.
First principles: what the trials say works
Three findings should shape any plan.
The best diet is the one you can keep. The DIETFITS trial randomised 609 adults to a healthy low fat or a healthy low carbohydrate diet for a year. Average loss was almost identical, 5.3 and 6.0 kg, and neither genotype nor insulin levels predicted which diet suited whom. Within each group, results ranged from 30 kg lost to 10 kg gained (Gardner et al., JAMA, 2018). What both successful groups had in common was that they cut sugar, refined flour and ultra processed food and ate more vegetables. Argue about macronutrients later.
Protein and fibre are the levers for hunger. Higher protein intakes of 1.2 to 1.6 grams per kilogram of body weight a day improve fullness, preserve muscle during weight loss and modestly increase calories burned in digestion (Leidy et al., American Journal of Clinical Nutrition, 2015). Fibre, at 30 grams a day, does the same at the other end of the meal. Together they are the difference between a deficit you can bear and one you cannot.
Exercise is for keeping it off, protecting muscle and your heart; diet is for losing it. The American College of Sports Medicine position stand found that 150 minutes a week of moderate activity produces only modest weight loss on its own, but 250 minutes and above produces clinically meaningful loss and, crucially, is the strongest predictor of keeping weight off long term (Donnelly et al., Medicine and Science in Sports and Exercise, 2009). Expecting exercise to do the losing is how Sam ended up with a swollen knee and a sense of failure.
How fast should you lose?
Half a kilogram to one kilogram a week, or around 0.5 to 1 percent of body weight, is the range guidelines recommend for most people. Faster loss is possible under supervision, as in the NHS total diet replacement programme, but comes with more muscle loss, a higher risk of gallstones and, as the Biggest Loser follow up showed, a bigger metabolic slowdown. A deficit of 500 to 750 calories a day below what you burn achieves it. For most men starting from a high weight, that means eating around 1,800 to 2,200 calories; for most women, 1,400 to 1,800. Going lower than 1,200 without medical supervision is a mistake. Know where you are starting from: our BMI calculator shows your category on both standard and Asian and Black thresholds and what a 5, 10 and 15 percent loss would look like for you.
The obesity diet: what to eat
Build every meal the same way
- Half the plate: vegetables or salad. Any kind, cooked any way that does not involve a batter. Frozen is fine. They provide volume, fibre and micronutrients for very few calories, and they slow the meal down.
- A quarter: protein. A palm sized portion, 25 to 40 grams of protein: chicken, turkey, fish, eggs, tofu, tempeh, Greek yoghurt, cottage cheese, lean beef, pulses. This is the piece most people under eat, especially at breakfast.
- A quarter: slow carbohydrate. A fist sized portion of potatoes, sweet potato, brown rice, oats, wholegrain bread, quinoa, beans or lentils. Not eliminated, just proportioned.
- A thumb of fat. Olive oil, nuts, seeds, avocado, a little cheese. Enough for flavour and fullness, not so much it swallows the deficit.
- Water, tea or coffee with the meal. No calories in the glass.
Foods to eat freely
All vegetables, salad leaves, berries, apples, pears, citrus, eggs, plain yoghurt, fish, poultry, pulses, oats, herbs, spices, vinegar, mustard, stock, tea, coffee, sparkling water. These are the foods that fill you up per calorie, and they are what the successful DIETFITS participants converged on regardless of which diet they were assigned.
Foods to remove from the house
Sugary drinks and juice, crisps, biscuits, confectionery, pastries, sweetened breakfast cereals, ice cream, takeaway more than once a week, and alcohol beyond a couple of drinks at the weekend. These are the ultra processed foods that led to an unnoticed 500 extra calories a day in the NIH ward study, and the rule is not "never" but "not in the house", because you will eat what is in the house at 10 pm and you will not drive to buy it. Bread, pasta and rice are not on this list; they are portioned, not banned.
A day that adds up to about 1,800 calories
| Meal | What | Protein | Calories |
|---|---|---|---|
| Breakfast | Two eggs scrambled with spinach and tomatoes, one slice wholegrain toast, coffee | 22 g | 380 |
| Mid morning | Greek yoghurt (170 g) with a handful of berries | 17 g | 170 |
| Lunch | Big salad with a tin of tuna or a cup of chickpeas, olive oil and vinegar, an apple | 30 g | 450 |
| Afternoon | A small handful of almonds, or a boiled egg and carrot sticks | 7 g | 170 |
| Dinner | Grilled salmon or chicken thigh, a fist of roast potatoes, half a plate of roasted vegetables | 38 g | 550 |
| Evening | Herbal tea, two squares of dark chocolate | 1 g | 110 |
Around 115 grams of protein, 32 grams of fibre, 1,830 calories, eight portions of vegetables and fruit. Sam ate some version of this most days for a year and says the surprise was that he was rarely hungry, which had never been true on any previous diet.
The habits around the food
- Eat breakfast with protein. Skipping it is fine for some people, but for most people with a lot to lose it leads to a 4 pm collapse into whatever is nearest.
- Sit down, use a plate, no screen. Eating from packets while distracted is where the extra calories hide.
- Front load the day. Bigger breakfast and lunch, smaller dinner, nothing after 8 pm most nights. Late eating is consistently linked with worse results.
- Sleep seven hours. Short sleep raises hunger hormones the next day and undoes willpower before you have used any.
- Weigh weekly, same day, same conditions. Track the trend, not the day. Weight fluctuates by 1 to 2 kg with water alone.
- Plan the slips. Everyone overeats sometimes. The difference between people who succeed and people who do not is that the successful ones have an ordinary breakfast the next morning rather than writing off the week.
Exercise for obesity: a plan that starts where you are
Every extra kilogram of body weight puts roughly four extra kilograms of force through the knees on each step, and eight on stairs. That is why running, jumping and high intensity circuits are the wrong starting point for someone carrying a lot of weight, however motivating the videos look. The goal of the first three months is not calories burned; it is building the joints, the tendons, the heart and the habit so that the calorie burning can happen later without injury.
Best exercises when you are obese
- Walking. Free, low impact, scalable, and the activity most strongly associated with long term maintenance in the National Weight Control Registry. Start with what you can do without pain, even five minutes, and add two minutes every few days.
- Water: swimming or aqua aerobics. The water carries most of your weight, so the joints are protected while the heart works hard. Many people with obesity find the pool the first place exercise feels good rather than punishing.
- Stationary or recumbent cycling. No impact, seated, and easy to control the intensity. A recumbent bike is the kindest option for bad backs and knees.
- Strength training. The most under prescribed exercise for obesity. It preserves muscle during weight loss, which protects your resting metabolism, and it makes the joints more resilient for everything else. It also produces visible strength gains within weeks, which keeps people going when the scales are slow.
- Chair based and floor exercises for people who cannot yet stand for long: sit to stand, seated marching, wall push ups, band rows.
A twelve week starting programme
| Weeks | Walking or cycling or pool | Strength | Weekly minutes |
|---|---|---|---|
| 1 to 2 | 10 minutes, 5 days a week, comfortable pace | Sit to stand from a chair, wall push ups, 2 sets of 8, twice a week | ~60 |
| 3 to 4 | 15 to 20 minutes, 5 days, slightly brisker | Add band rows and a step up on the bottom stair, 2 sets of 10 | ~90 |
| 5 to 6 | 25 minutes, 5 days; one day slightly longer | 3 sets of 10; add a supported squat to a box | ~130 |
| 7 to 8 | 30 minutes, 5 days, brisk enough that talking takes effort | Add a light dumbbell press and a hip hinge with a broomstick | ~160 |
| 9 to 10 | 35 minutes, 5 days; consider a pool or bike session as one of them | 3 sets of 12, increase weights when the last rep is easy | ~190 |
| 11 to 12 | 40 minutes, 5 to 6 days | Two full body sessions of 25 minutes | ~240 |
After twelve weeks you are at the 250 minute threshold where exercise starts to contribute meaningfully to weight loss and, more importantly, to keeping it off. From there, add intensity slowly: hills, intervals of faster walking, heavier weights. Running, if you want it, becomes reasonable once you are within 15 kg or so of a healthy weight and have three months of strength work behind you. Sam started jogging at month nine and ran a 10K at month fourteen. He still thinks the pool was the thing that saved him.
Three rules that prevent injury
- Increase by no more than 10 percent a week. Total minutes, distance or load. Tendons adapt slower than lungs.
- Pain that changes how you move means stop. Muscle soreness the next day is fine; joint pain during exercise is not.
- Shoes matter more when you are heavier. Get fitted, replace them every 600 to 800 km, and if your feet ache, see a podiatrist before you give up.
If you are on a weight loss medicine
Semaglutide, tirzepatide and their successors make the diet side dramatically easier and the exercise side more important, because a quarter to a third of the weight lost on them is lean tissue unless you actively protect it. The evidence based response is the same plan as above with two emphases: hit the protein target every day even when appetite is low, which may mean protein at every meal and a shake if needed, and do the strength sessions without fail. People who do both lose mostly fat; people who do neither lose muscle they will regret. Our guide to obesity treatment covers the medicines in detail.
Keeping it off: the part nobody plans for
The National Weight Control Registry has followed more than 10,000 people who lost at least 13 kg and kept it off for at least a year. Their habits are boringly consistent: they eat breakfast, they weigh themselves at least weekly, they watch less than ten hours of television a week, they eat a similar diet on weekdays and weekends, and they average about an hour of physical activity a day, mostly walking. None of it is heroic. All of it is permanent. After weight loss your body will be hungrier and burn fewer calories than a person who was never heavy at the same weight; that is the biology described in our causes and prevention article, and it is why maintenance is an active practice rather than a return to normal. The good news is that the practice gets easier, because the habits become the life.
What Sam would say
He would say that the plan that worked was slower, gentler and more boring than any plan that failed, and that this was the point. He would say get in the pool before you buy the running shoes. He would say eat the eggs. He would say that the scale is information, not judgement, and that the week he stopped hating himself was the week the weight started coming off and stayed off. And he would say that if it feels like your body is fighting you, that is because it is, and there is no shame in getting medical help with the fight. He is 96 kilograms today, two years steady, and he keeps the old running shoes in the cupboard as a reminder that the problem was never him.
Read next
- How to prevent obesity: causes, risk factors and what actually works
- Obesity treatment: can obesity be cured? Diet, medicines and surgery compared
- BMI calculator with Asian and Black thresholds
- Gallstone diet and exercise: what to eat and how to move
Frequently asked questions
What is the best diet for obesity?
The one you can sustain. In the largest head to head trial, healthy low fat and healthy low carbohydrate diets produced the same results. What matters is cutting ultra processed food, sugary drinks and refined flour, eating plenty of vegetables, and getting 1.2 to 1.6 g/kg of protein and 30 g of fibre a day to control hunger.
What is the best exercise for an obese person?
Walking, swimming or water exercise, cycling and strength training. These protect the joints while building fitness and muscle. Running and high impact classes are best left until weight is lower and three months of strength work are behind you.
How many calories should an obese person eat to lose weight?
Around 500 to 750 below what you burn, which for most people starting from a high weight means 1,800 to 2,200 calories for men and 1,400 to 1,800 for women, producing 0.5 to 1 kg a week. Below 1,200 needs medical supervision.
How do I lose weight when I am obese and cannot exercise?
Weight loss comes mainly from diet, so start there. Chair based movement, pool exercise and short walks can be added as the joints allow, and physiotherapy referral is worthwhile. Losing the first 5 to 10 percent often makes movement possible that was not before.
This article is for general information and does not replace advice from your own doctor, dietitian or physiotherapist, especially if you have joint problems, heart disease, diabetes or are on weight loss medication.
