Weight loss that lasts: losing fat, keeping muscle, and keeping it off

Overweight and obesity, and why they matter

About 4 in 10 American adults have obesity. Excess body fat, and especially the visceral fat stored around the organs, drives insulin resistance, which in turn drives fatty liver, high blood sugar, high triglycerides and high blood pressure. That’s why weight is the common lever for all of them.

Measuring it: beyond the scale

The scale mixes fat, muscle, water and glycogen. A DXA scan shows whether you’re actually losing fat and keeping muscle, which is the whole point. See What is a DXA Scan? and real client results measured by DXA.

Why 5–10% is the number to aim for first

In people with overweight and type 2 diabetes, losing just 5–10% of body weight meaningfully improved blood sugar, blood pressure, triglycerides and HDL cholesterol, and larger losses brought larger benefits. You don’t need to reach a "goal weight" to get healthier.

How to lose fat, not muscle

1. A moderate deficit at a sustainable pace

Energy balance is the foundation: you lose weight when you take in less energy than you use. But the pace matters. Losing about 0.5–1% of body weight a week preserves more muscle, keeps training quality up and lets you eat filling meals. Crash diets mostly lose water and glycogen at first, cost more muscle, and tend to snap back. See How Fast Can I Lose Fat?

2. Enough protein

Protein is the most filling nutrient, takes the most energy to digest, and protects muscle in a deficit. A good range for most active people losing weight is 1.6–2.2 g per kg of body weight a day. Hitting it consistently matters more than hitting it perfectly.

3. Resistance training

Lifting weights (or other resistance training) is the signal that tells your body to keep its muscle while it loses fat. Pair it with enough protein and the weight you lose comes mostly from fat.

4. Fiber, whole foods and a supportive environment

Fiber and minimally processed foods fill you up for fewer calories; in a tightly controlled trial, people ate about 500 more calories a day on an ultra-processed diet. Set up your kitchen, office and car so the easy choice is the good one (see Nutrition Architecture).

5. A plan that fits your life

In the DIETFITS trial, healthy low-fat and healthy low-carb diets produced almost the same weight loss after a year. The best diet is the one that fits your schedule, preferences and culture, and that you can repeat on busy weeks, holidays and travel.

Weight loss medications (GLP-1s)

GLP-1 medications like semaglutide and tirzepatide are the most effective obesity medications we have, and they work best with good nutrition and training alongside them. You may have heard they cause muscle loss. Here’s the fuller picture.

• Losing muscle isn’t unique to these drugs. Any long stretch of eating less than you burn costs some muscle unless something tells the body to keep it, and resistance training is that signal. A 2026 review of 20 randomized trials found that lean mass made up a similar share of the weight lost with these medications (about 25–35%) as with diet-and-lifestyle programs (about 26%), and the smallest share (about 18%) when lifestyle programs included resistance training.
• The big drug trials didn’t include resistance training. Participants got diet counseling and a general goal of about 150 minutes of activity a week, or, in one study, no exercise guidance beyond usual care. No one was lifting on a structured program, so these trials show what happens without the one thing best proven to protect muscle.
• "Lean mass" overstates muscle loss. The lean mass a DXA scan reports includes water, glycogen, organs and connective tissue; skeletal muscle is only about half of it. Studies that measured muscle directly with MRI found thigh muscle fell roughly in line with the amount of weight lost, while fat stored inside the muscle went down, a sign of better muscle quality. Short-term studies have found grip strength and sit-to-stand performance generally held up.
• Resistance training works during weight loss. In diet studies, adding resistance training prevented most of the lean mass loss in older adults with obesity. With a GLP-1 medication, in people who had just lost weight on a low-calorie diet, liraglutide plus a supervised exercise program (mostly vigorous cardio with some circuit training) preserved lean mass and produced about twice the fat loss of either one alone. Trials of semaglutide and tirzepatide with structured resistance training are under way.
• Still to learn: long-term strength and function data, especially for older adults, who have less muscle to spare.

The takeaway isn’t to avoid these medications; it’s to use them well. Because they blunt appetite so much, it’s easy to under-eat protein. Prioritize protein, lift weights two to three times a week, and build eating habits you can keep if the medication is ever reduced or stopped.

Keeping it off

Weight regain is common when the methods used to lose weight look nothing like real life. The more your weight-loss phase resembles a routine you could keep (normal foods, flexible meals, room for social life), the easier the move to maintenance. Plan that transition before you reach your goal, not after.