How to lose weight: the definitive science-based guide (2026)

The plan in 5 steps

If you only read one part of this guide, make it this one. Each step has its own section below with the figures and the studies, plus a link to the article that develops it:

1. 1

   1. Work out how much you burn

   Your maintenance (TDEE): a starting estimate that your scale corrects later.

2. 2

   2. Create a moderate deficit

   300-550 kcal less a day: about 0.25-0.5 kg a week at first, without going below 1,200 kcal (women) or 1,500 kcal (men).

3. 3

   3. Eat enough protein

   At least 1.6 g per kilo of body weight, spread over 3-4 meals.

4. 4

   4. Strength-train and move

   Strength training 2-3 days a week and 150-300 minutes of moderate activity a week.

5. 5

   5. Sleep and track the trend

   7 hours of sleep or more, and your weekly average weight as the reference. Recalculate every 4-5 kg.

Why it is simple but not easy

If you eat less energy than you burn, your body draws on its reserves, mostly fat, and you lose weight. What is hard is everything else: hunger, tiredness, eating out, short sleep. And there is a nuance worth knowing from the start: weight responds slowly. The model by Hall et al. (Lancet 2011) calculates that after a sustained change in what you eat, your weight takes on the order of a year to cover half the distance to its new equilibrium, because as you lose weight you also burn less. That is why diets lasting a few weeks disappoint, and why this guide keeps coming back to what you can sustain on an ordinary Tuesday a year from now.

Step 1. Work out how much you burn (your TDEE)

Your total daily expenditure, or maintenance, is what you would need to eat to neither gain nor lose weight. Most of it is your basal metabolism (what you burn at rest just to stay alive); the rest is digestion and, above all, movement. The most widely used equation is Mifflin-St Jeor, published in 1990 from 498 adults whose resting expenditure was measured by calorimetry: it estimates your basal rate, which you then multiply by an activity factor. The TDEE calculator does the maths and, if you have already spent a few weeks logging what you eat and weighing yourself, it also gives you your real maintenance.

• Men: basal = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
• Women: basal = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
• Activity factor: sedentary 1.2; exercise 1-3 days a week 1.375; 3-5 days 1.55; 6-7 days 1.725
• The result is an estimate, not a measurement: two people with the same data can burn different amounts. That is why, after 2-3 weeks, you correct it with the real trend of your weight

A worked example

Maria is 34, weighs 68 kg, is 164 cm tall and trains 3 times a week. Basal = 680 + 1,025 − 170 − 161 = 1,374 kcal. Maintenance = 1,374 × 1.55 = about 2,130 kcal. With a 400 kcal deficit, her target is about 1,730 kcal a day, and the classic rule gives her about 0.36 kg a week at first (400 × 7 ÷ 7,700), roughly 1.5 kg a month. If after three weeks her average weight has dropped much less, the most likely explanations are that she eats more than she logs or that her real expenditure is lower than estimated: that is where she adjusts. For the mechanics of logging, see how to count calories without going crazy.

Step 2. Create a moderate deficit

The starting arithmetic is the classic rule: one kilo of weight lost equals about 7,700 kcal (a kilo of pure fat holds more, but fat tissue also contains water). By that rule, every 0.25 kg a week needs a deficit of about 275 kcal a day. A moderate deficit of 300-550 kcal is a reasonable starting point for most people: it shows on the scale within a few weeks, hunger stays manageable and it leaves room to eat protein and train. The AHA/ACC/TOS guideline (Jensen et al., 2013) for adults with overweight or obesity talks about deficits of 500-750 kcal, or diets of 1,200-1,500 kcal (women) and 1,500-1,800 kcal (men); below 800 kcal, only with medical supervision. The full detail, with three worked examples and the table by pace, is in caloric deficit for beginners.

How low to go, and how fast

Without medical supervision, treat 1,200 kcal (women) and 1,500 kcal (men) as a floor: if the pace you want takes you below it, choose a slower one or add activity. The CDC considers losing 1-2 pounds a week (0.45-0.9 kg) gradual, and that is a ceiling, not a target: for most people, 0.25-0.5 kg a week is easier to sustain. If you are pregnant or breastfeeding, under 18, have a medical condition or have had an eating disorder, talk to a health professional first. On shortcuts: how fast you can lose weight safely.

Step 3. Protein: make sure what you lose is fat

In a deficit, the body can also break down muscle, and what holds that back is enough protein plus strength training. The EFSA reference for adults, 0.83 g per kilo, covers almost everyone’s needs, but it was not designed to preserve muscle while dieting. In the meta-analysis by Morton et al. (Br J Sports Med 2018; 49 trials, 1,863 people doing strength training), gains in fat-free mass stopped increasing at around 1.6 g/kg a day, with an interval reaching 2.2 g/kg. The ISSN (Jäger et al., 2017) gives a general range of 1.4-2.0 g/kg and raises it to 2.3-3.1 g/kg for resistance-trained people in a deficit. In practice: at least 1.6 g/kg, spread over 3-4 meals. For 68 kg, that is about 109 g a day.

What is more, protein is the macronutrient that costs the most to digest: 20-30% of its calories are spent processing it, compared with 5-10% for carbohydrates and 0-3% for fat (Westerterp, 2004). And in the trial by Longland et al. (2016), with a steep deficit and training 6 days a week, the group on 2.4 g/kg gained 1.2 kg of lean mass and lost 4.8 kg of fat in 4 weeks; the group on 1.2 g/kg, 0.1 kg and 3.5 kg. In adults with healthy kidneys, trials do not show kidney damage from high intakes; if you have kidney disease, your doctor decides the amount. The table by weight and goal is in how much protein you need, and your exact figure in the protein calculator.

Step 4. Strength training and daily movement

Exercise is not the main lever for losing weight: diet is. The review by Thomas et al. (Obes Rev 2012) looked at why exercise programmes without dieting produce less weight loss than the calories burned would predict, and concluded that it is mainly down to low doses of exercise and to people ending up eating a little more. But exercise decides what you lose and how you keep it off. The WHO recommends that adults do 150-300 minutes of moderate aerobic activity a week (or 75-150 of vigorous activity) and muscle-strengthening exercise on at least 2 days a week. In the meta-analysis by Wewege et al. (Sports Med 2022; 58 studies), strength training alone, without dieting, lowered body fat percentage by 1.46 points and body fat by 0.55 kg compared with not training, and visceral fat too.

A realistic plan: 2-3 full-body strength sessions a week, with exercises that move several joints (squat, deadlift or hip hinge, pushes and pulls), and on the other days, walking or cardio you enjoy. If you are starting from zero, our gym routine for beginners has a 3-day plan with little equipment, and cardio vs weights has the full comparison.

The least visible lever: moving outside the gym

Movement that is not sport (walking, climbing stairs, standing, running errands) is called NEAT, and it varies a lot from person to person. In the study by Levine et al. (Science 2005), 10 people with mild obesity spent on average 2 hours more a day sitting than 10 lean people; if they adopted the lean group’s movement habits, they would burn about 350 kcal more a day. Muscle, by contrast, burns less than people repeat: about 13 kcal a day per kilo at rest (Wang et al., 2010), not 50-70. Its value is that it lets you move and train more and protects your expenditure while you lose weight. We explain it in how to speed up your metabolism.

Step 5. Sleep, manage stress and measure properly

Short sleep makes dieting an uphill battle. In the study by Spiegel et al. (Ann Intern Med 2004), 12 young men who slept 4 hours for two nights had 18% lower leptin (which curbs hunger), 28% higher ghrelin (which triggers it) and 24% more hunger. In a meta-analysis of 11 studies (Al Khatib et al., 2017), cutting sleep made people eat about 385 kcal more a day without burning more. And in the trial by Nedeltcheva et al. (Ann Intern Med 2010), 10 adults with overweight followed the same diet for 14 days sleeping 8.5 or 5.5 hours: they lost a similar amount of weight, but with 5.5 hours only 0.6 kg of it was fat, compared with 1.4 kg, and they lost more fat-free mass (2.4 vs 1.5 kg). The reference for adults is 7 hours of sleep or more; more detail in how sleep affects your weight.

With stress, it pays not to exaggerate in either direction. Chronic stress is associated with weight gain, but the measured effect is small: that was the conclusion of a meta-analysis of longitudinal studies (Wardle et al., Obesity 2011). Where it weighs most is in what it pushes you to eat and the sleep it takes away, not in a “cortisol belly”: we cover it in stress, cortisol and weight. If you notice that you eat without physical hunger, out of anxiety or boredom, emotional hunger vs real hunger explains how to tell them apart and what works.

How to measure your progress without going crazy

• Weigh yourself under the same conditions (in the morning, after using the toilet) several days a week and compare the 7-day average with the previous week’s. Weight on a single day swings 1-2 kg with water, salt, glycogen or the menstrual cycle
• Measure your waist at navel height every 2-4 weeks: it reflects abdominal fat better than the scale. The waist-to-height ratio calculator tells you where you stand
• Take front and side photos every 4 weeks, with the same light and the same clothes
• Write down your loads in 3-4 exercises: if you keep or increase your strength while your weight drops, you are holding on to muscle
• If after 3 weeks your weekly average has not moved, review your log before cutting further: that is usually where the gap is

Which diet to choose: the split matters less than being able to stick to it

When calories and protein are matched, branded diets produce similar weight loss. In the POUNDS Lost trial (Sacks et al., NEJM 2009), 811 adults followed four diets with different proportions of fat, protein and carbohydrate for 2 years, and weight loss was similar on all of them. In DIETFITS (Gardner et al., JAMA 2018), 609 adults on a low-fat or a low-carb diet, with no calorie target set, lost 5.3 and 6.0 kg in 12 months, with no significant difference. And in the meta-analysis by Hall and Guo (2017), covering 32 controlled feeding studies, cutting carbs at equal calories did not cause more fat loss. What decides it is whether you can sustain it. Set your protein first and split the rest: EFSA puts fat at 20-35% of energy, and the macro calculator gives you the grams. If you want to understand each macro, read what macronutrients are.

On intermittent fasting, the trials are clear: in TREAT (Lowe et al., 2020; 116 adults, 12 weeks), eating from 12:00 to 20:00 with no other guidance did not produce more weight loss than three meals a day; and in the trial by Liu et al. (NEJM 2022; 139 people, 12 months), adding an 8-hour window to a calorie-restricted diet gave 8.0 vs 6.3 kg, a difference that was not significant. It works if it makes you eat less; the full detail is in the 16:8 fasting guide. If you do not want to count anything, the Harvard plate method is a good shortcut: half the plate vegetables and fruit, a quarter protein and a quarter whole grains. And to help the plan survive the week, it pays to cook ahead (meal prep for beginners) and organise it with the weekly menu template.

Why you stop losing weight (and what to do)

There will come a point when your average weight stays still for 2-3 weeks even though you are doing the same things. It is almost always a mix of three things. First: your expenditure has dropped (about 24 kcal a day per kilo lost) and your deficit has shrunk. Second: your logging has slipped. In the study by Lichtman et al. (NEJM 1992), ten people who said they could not lose weight on less than 1,200 kcal had an expenditure within 5% of the expected value; what was failing was the log: they under-reported what they ate by 47% on average and overestimated their activity by 51%. Third: water retained because of salt, stress, the menstrual cycle or a new training plan, which can hide fat loss for a while. The full guide is in how to break a weight loss plateau.

And the “broken” metabolism? The most cited case is 14 contestants from “The Biggest Loser” (Fothergill et al., Obesity 2016): they lost an average of 58 kg in 30 weeks with extreme diet and exercise, and 6 years later, after regaining 41 kg, their resting expenditure was still about 500 kcal a day below what was expected for their body composition. The authors describe it as a proportional, though incomplete, adaptation to the weight still being kept off, and that adaptation did not predict who regained more weight. It is an extreme case, not what happens to someone who loses 8 kg in six months. What to do about a plateau:

• Recalculate your maintenance at your current weight: after losing 5 kg it may have dropped by about 120 kcal
• Log carefully for 7 days in a row, weekend included, weighing oils, sauces, drinks and snacks
• Add steps before cutting food: it is easier to sustain than going below the prudent floors
• If you have been in a deficit for months, spend 1-2 weeks at maintenance. In the MATADOR trial (Byrne et al., 2018), 51 men with obesity dieted for 16 weeks: those who alternated 2-week blocks of dieting with 2 weeks at maintenance lost more weight (14.1 vs 9.1 kg) and more fat (12.3 vs 8.0 kg), although it took them 30 calendar weeks instead of 16. It is a single trial, in men
• Do not go lower if you are already at the floor (1,200 kcal for women, 1,500 kcal for men): accept a slower pace or move more

The mistakes that hold people back most

These are the patterns that come up most often among people who are “doing everything right” and see no change. Food figures come from USDA FoodData Central:

• Not counting oil: one tablespoon of olive oil (13.5 g) is 119 kcal. Two or three a day add up to 240-360 kcal you cannot see on the plate
• Forgetting drinks: a coffee with 150 ml of whole milk and two teaspoons of sugar comes to about 130 kcal; a cup (248 g) of orange juice, 112; a 355 ml can of beer, 153; a 150 ml glass of red wine, about 125. Your base drink should be water: how much you need is in how much water to drink per day
• Snacking without logging it: 23 almonds (28 g) are 164 kcal. Three or four of those a day already add up to a whole snack
• Switching off at the weekend: if from Monday to Friday you eat 500 kcal below your maintenance (2,500 kcal in total), a Saturday with 1,000 kcal extra and a Sunday with 1,500 wipe out the week’s deficit
• Trusting the product name: “light”, “natural” or “fit” do not tell you how many calories it has. Check the label per 100 g and per serving: we explain how in how to read nutrition labels

Myths you can forget

Four that do not stand up to the studies. On belly fat, see how to lose belly fat.

Keeping the weight off: the phase that decides

Regaining lost weight is common. In a meta-analysis of 29 US studies (Anderson et al., Am J Clin Nutr 2001), people who lost weight on conventional calorie-restricted diets were keeping off, on average, only 17% of what they had lost after 5 years. And speed does not seem to be the cause (see the FAQ). But regain is not inevitable. In the National Weight Control Registry (Thomas et al., Am J Prev Med 2014), 2,886 people who had lost at least 13.6 kg (30 lb) and kept it off for a year were still, on average, 23 kg below their maximum weight after 10 years, and more than 87% were keeping off at least 10% of their weight at 5 and at 10 years. It is a registry of people who had already succeeded, not a random sample, but it is a guide: those who regained most were the ones who cut back their physical activity, weighed themselves less often and relaxed their control over what they ate.

• Come off the diet gradually: your new maintenance is lower than before because you weigh less. Raise your calories in small steps and stay a couple of weeks on each one, watching the weekly average
• Keep weighing yourself regularly: it is the early warning that lets you correct 1-2 kg before they become 5
• Keep up strength training and daily movement: a drop in activity was among the things most associated with regaining weight

Why it happens and what really helps, with the studies on appetite after weight loss, is in the rebound effect: how to avoid it.

If you have hypothyroidism or PCOS, or take a GLP-1 medicine

The principles are the same (deficit, protein, strength training, sleep), but there are nuances your doctor should know about and supervise:

Hypothyroidism

Thyroid hormone is one of the main regulators of basal metabolism, and untreated hypothyroidism can lower your expenditure. With well-adjusted treatment, the plan usually works the same way. It is not diagnosed from the scale or from a few loose symptoms: it takes a blood test that a doctor interprets, and you should never change your medication on your own. What to eat is covered in hypothyroidism and weight.

Polycystic ovary syndrome (PCOS)

Insulin resistance is common in PCOS, especially with excess weight. The Endocrine Society guideline (2013) considers lifestyle changes, a lower-calorie diet and exercise, beneficial for women with PCOS and overweight because of their effect on general health, although it notes that it is unclear how much weight loss improves PCOS itself. The rest of the plan is the same.

GLP-1 treatments (semaglutide, liraglutide, tirzepatide)

These medicines have changed the treatment of obesity. In the STEP 1 trial (Wilding et al., NEJM 2021), 1,961 adults with obesity or overweight treated with weekly semaglutide, together with lifestyle changes, lost an average of 14.9% of their body weight over 68 weeks, compared with 2.4% on placebo. Part of what is lost in any large weight loss is lean mass, so it makes sense to look after your protein and keep strength training while on the medicine too. Your doctor decides the regimen and the dose; what to eat during treatment is covered in Ozempic, GLP-1 and diet.

How Renzy helps

The step that fails most often is knowing how much you really eat. With Renzy you take a photo of your plate and get an estimate of calories and macros that you can correct before saving it, and for packaged food there is the barcode scanner. The estimate is just that, an estimate: check the portion, especially on large plates, and add by hand what you cannot see, such as oil. Renzy has a 7-day trial that requires a card and there is no free plan: if you cancel before it ends, you pay nothing. Where this technology is heading is covered in artificial intelligence and nutrition.