Weight-Loss Injections vs Diet and Exercise: What the Trials Show

Are weight-loss injections better than diet and exercise?

On average, yes, for the amount of weight lost in trials, but the trials did not compare a drug with diet and exercise. In the main trials of semaglutide (the medicine in Wegovy and Ozempic) and tirzepatide (the medicine in Mounjaro), everyone, including the placebo group, had diet and activity goals, so the drug's effect was measured on top of lifestyle change, not instead of it. The placebo groups were, in effect, diet-and-exercise groups, and they lost 2–3% of their body weight.

Whether a prescription medicine is right for you is the prescribing doctor's decision, based on your BMI, health conditions and history. What you control is the eating, walking and strength work every one of these trials paired with the drug, which diet-and-exercise trials show can work on its own, with smaller average losses.

What did the Wegovy and Mounjaro trials show?

The Wegovy trial, STEP 1 (Wilding et al., New England Journal of Medicine, 2021), enrolled 1,961 adults without diabetes who had a BMI of 30 or more, or 27 or more with at least one weight-related condition. They took weekly semaglutide 2.4 mg or a placebo for 68 weeks, both plus lifestyle intervention. The mean change in body weight was a 14.9% loss with semaglutide against 2.4% with placebo: 15.3 kg against 2.6 kg. Half (50.5%) on semaglutide lost at least 15%, against 4.9% on placebo.

The tirzepatide trial, SURMOUNT-1 (Jastreboff et al., New England Journal of Medicine, 2022), enrolled 2,539 adults without diabetes on the same BMI rules, with an average starting weight of 104.8 kg and an average BMI of 38.0. They took weekly tirzepatide at 5, 10 or 15 mg, or a placebo, for 72 weeks. The mean losses were 15.0% at 5 mg, 19.5% at 10 mg and 20.9% at 15 mg, against 3.1% with placebo.

For Indian readers, a relevant trial is STEP 11 (Lancet Diabetes and Endocrinology, 2025). It tested semaglutide 2.4 mg in 150 adults of Asian descent in South Korea and Thailand, with obesity defined as a BMI of 25 or more, the cut-off many Asian populations use because health risks rise at lower BMIs. With a reduced-calorie diet and increased physical activity in both groups, the mean change at 44 weeks was a 16.0% loss with semaglutide against 3.1% with placebo. It did not include India.

Were these drug trials on top of diet and exercise?

Yes. STEP 1 describes semaglutide ‘plus lifestyle intervention’. A 2026 review of 42 phase 3 trials of FDA-approved weight-loss medicines, including STEP 1 and SURMOUNT-1 (Chao et al., Obesity Science and Practice), concluded that lifestyle interventions have been core components of these trials. Most set a goal of eating about 500 kcal a day less than the body needs, and the most common activity goal was at least 150 minutes a week. Of the 42 trials, 22 provided counselling at least monthly and 16 more at least every three months.

How much weight can you lose with diet and exercise alone?

In Look AHEAD, a large trial of an intensive diet-and-exercise program, people lost an average of 8.6% of their weight in a year, with measurable health changes. It randomised 5,145 adults aged 45–74 with type 2 diabetes and a BMI over 25 to an intensive lifestyle program of group and individual meetings aimed at eating less and moving more, or to diabetes support and education. At one year the lifestyle group had lost 8.6% of starting weight against 0.7%, their fitness had risen 20.9% against 5.8%, and average A1C fell from 7.3% to 6.6%.

Over eight years the gap narrowed but held. With counselling continuing, the lifestyle group was 4.7% lighter than at the start, against 2.1% for the comparison group. Half the lifestyle group (50.3%) were still at least 5% lighter at year 8 and 26.9% were at least 10% lighter, against 35.7% and 17.2%. Key weight-control behaviours separated those who lost 10% and kept it off from those who regained.

The Diabetes Prevention Program (Knowler et al., New England Journal of Medicine, 2002) tested a lifestyle program in 3,234 adults with raised blood glucose, with goals of at least a 7% weight loss and 150 minutes of activity a week. Over an average of 2.8 years, the lifestyle program reduced new cases of type 2 diabetes by 58% compared with placebo, against 31% for the drug metformin.

By our arithmetic, 8.6% of a 90 kg starting weight is about 7.7 kg in a year. To see where you start, check your BMI with the BMI calculator and your daily energy needs with the TDEE calculator.

How do injections and diet and exercise compare, side by side?

The gap between drug and placebo in each drug trial, 12.4 percentage points in STEP 1, is the drug's added effect over the same lifestyle advice. The placebo groups lost less than Look AHEAD's intensive lifestyle group, a hint that the amount of lifestyle support may matter, though Look AHEAD enrolled people with type 2 diabetes and the drug trials excluded them.

Who are weight-loss injections approved for?

In the US, the FDA approved tirzepatide for chronic weight management, as Zepbound, on 8 November 2023 for adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition such as high blood pressure, type 2 diabetes or high cholesterol, in addition to a reduced-calorie diet and increased physical activity. STEP 1 and SURMOUNT-1 used the same BMI thresholds. The FDA says tirzepatide should not be used by people with a personal or family history of medullary thyroid cancer, or with Multiple Endocrine Neoplasia syndrome type 2.

In India these are Schedule H medicines, which are supposed to be sold only against a prescription, according to the April 2026 PTI report. Whether a lower Asian BMI cut-off like STEP 11's applies to you is for your doctor, working from the Indian prescribing information and your whole health picture.

Should you choose injections or diet and exercise?

Every drug trial above added the drug to diet and activity goals, and the FDA approved tirzepatide on the same terms. Two concerns explain why exercise and food still matter once a medicine is prescribed.

The first is muscle. Dr Ambrish Mithal of Max Healthcare, quoted in the April 2026 PTI report, said the bigger concern is muscle loss, which can account for 20–30 per cent of total weight lost if diet and exercise are neglected, and linked it to unstructured weight loss without adequate protein intake, strength training and medical supervision. Our guide to exercise on weight-loss injections covers how to train to keep muscle, and protein on weight-loss injections covers eating enough on a small appetite.

The second is stopping. The STEP 1 extension (Wilding et al., Diabetes, Obesity and Metabolism, 2022) followed 327 participants for a year after both the drug and the lifestyle program ended at week 68. Those on semaglutide had lost 17.3% and regained 11.6 percentage points by week 120, leaving a net loss of 5.6%. The authors call this regaining two-thirds of the prior weight loss. Dr Saptarshi Bhattacharya, quoted in the same PTI report, warned that short-term use without sustained lifestyle changes may lead to rebound weight gain after discontinuation. The extension did not test whether keeping up exercise prevents regain; our guide on keeping weight off after stopping looks at what the evidence says.

Can I lose weight without Ozempic or Mounjaro?

Many people can, but the average loss in trials is smaller than on the drugs. Look AHEAD's lifestyle group averaged 8.6% at one year and half were still at least 5% lighter after eight years. A fair attempt uses what the trials used: a measured deficit, an activity target, records and review. Get your doctor's go-ahead first if you have a health condition.

1. 1

   Know your starting numbers

   Record your weight, waist and BMI, and work out your daily energy needs. Weigh once a week at the same time of day and watch the trend.

2. 2

   Set a modest calorie deficit

   Most of the 42 trials in the 2026 review set a goal of about 500 kcal a day below needs. Use the calorie deficit calculator to find yours, and build meals around a protein food and vegetables.

3. 3

   Build up to 150 minutes of activity a week

   This was the Diabetes Prevention Program's goal and the most common one in the drug trials. Brisk walking counts; add 10 minutes a week until you get there.

4. 4

   Add strength training

   Our coaches program two or three short sessions a week of squats, hinges, pushes, pulls and carries, adding load slowly, with your form checked on camera.

5. 5

   Keep simple records

   Many trials asked for food and activity diaries. A phone note of meals, steps, sessions and weekly weight is enough.

6. 6

   Review at 12 weeks

   Take your records to your doctor; the trials ran 44 weeks or longer, so judge over months. If the scale hasn't moved, check the usual causes in not losing weight in a calorie deficit before deciding anything. If you have type 2 diabetes, see exercise for type 2 diabetes.

What can these trial comparisons not tell you?

• Different people. Look AHEAD enrolled adults aged 45–74 with type 2 diabetes; the Diabetes Prevention Program enrolled people with raised blood glucose; STEP 1 and SURMOUNT-1 excluded diabetes.
• Different support. Look AHEAD's intensive program used group and individual meetings, while most of the drug trials in the 2026 review offered counselling at least monthly or every three months.
• Averages hide a range. In STEP 1, 86.4% on semaglutide lost at least 5%, which means, by our arithmetic, about 1 in 7 did not.
• Side effects and stopping. In STEP 1, 4.5% on semaglutide stopped because of gut side effects, against 0.8% on placebo. In SURMOUNT-1, 4.3–7.1% on tirzepatide stopped because of side effects, against 2.6%.
• Funding. STEP 1 was funded by Novo Nordisk and SURMOUNT-1 was supported by Eli Lilly, the makers of the two medicines.
• Few Asian, and no Indian-only, results here. STEP 11 tested semaglutide in South Korea and Thailand; we did not find an India-only trial to cite.

What should you ask your doctor about weight-loss injections?

• Do I meet the criteria for a weight-loss medicine, and is one appropriate with my other conditions and medicines?
• What diet and activity changes should go with it, and are there limits on exercise while I start?
• How long would I take it, and what is the plan if or when it stops?
• Which side effects mean I should call you, and which mean I should skip training that day?
• If I try diet and exercise first, for how long, and what result should we review it against?

Where a coach fits, with or without an injection

MakeMyFitness is live one-to-one coaching on video for people in India, at ₹799 a session at your own gym or ₹899 at home, and it suits someone who wants the exercise and food side of weight loss done properly, whether or not their doctor has prescribed a medicine. The coach watches your form on camera, sets the strength work and walking targets, and checks your protein and calorie numbers against your fat loss goal. You can train at home with Personal Home Training or at your own gym with Personal Gym Training.

Our coaches, led by Kumar Abhishek, are fitness coaches, not doctors, dietitians or physiotherapists. We don't advise on whether to take a medicine, at what dose, or when to stop it, and we follow any limits your doctor sets. Rehab & Recovery is coaching after a clinician has cleared you, not treatment. Read our medical disclaimer, and if you are weighing doctor-led plans against coaching, see online weight loss programs in India compared.