True: “Lifting weights while losing weight protects your muscle.”

True

Evidence confidence Moderate

The short answer

Lifting weights while you lose weight cuts how much muscle you lose, though it does not always prevent the loss completely.

What this means for you

If you are losing weight, lifting is one of the best-supported ways to limit how much muscle you lose with the fat; eating enough protein and keeping your calorie cut modest help too. You do not need to fear cardio; it will not burn your muscle off, it just will not protect it the way lifting does. Judge progress by your waist, your strength and how your clothes fit, since the scale cannot tell muscle from fat.

Your next step

Add two or three full-body lifting sessions a week to whatever eating plan you follow, and keep your protein up.

Why this confidence?

A meta-analysis of 6 randomized trials, a large 6-month randomized trial and a 114-trial meta-analysis all found that lifting during a calorie deficit keeps much of the muscle that dieting alone strips away, with no cost to fat loss, though lifters in the 6-month trial still lost some. The direct trials are mostly in older adults with obesity, so the exact numbers in younger people are less certain.

The facts

Lifting weights while you lose weight cuts how much muscle you lose, though it does not always prevent the loss completely. In pooled trials of older adults on a diet, those who lifted three times a week held their muscle steady (up about 0.1 pound) while the diet-only groups lost about 1.7 pounds, and both groups lost about the same fat and weight. In a larger 6-month trial, dieters who lifted still lost about 2 pounds of muscle, about a third as much as those who did only cardio, and those doing both cardio and lifting gained the most in everyday physical function. How much protein you eat and the size of your calorie cut also affect how much muscle you keep.

The bigger picture

In the 6-month randomized trial of 160 obese adults over 65 on a diet with a 500 to 750 calorie-a-day deficit, the lifting group lost about 2 pounds of muscle, the cardio-plus-lifting group about 3.7, and the cardio-only group about 6, while all three lost about the same weight (19 to 20 pounds) and about the same fat. Hip bone density fell 0.5 percent with lifting and 3 percent with cardio alone, and strength rose 18 to 19 percent in the lifting groups versus 4 percent with cardio. Across 114 randomized trials in people with overweight or obesity, lifting plus eating less cut about 12 pounds of fat with muscle held flat. Cardio does not burn muscle: 8 months of cardio alone with no diet change left muscle unchanged, and adding cardio to a lifting program did not reduce muscle growth across 43 studies. But cardio does not protect muscle on a diet the way lifting does; the diet, not the cardio, is what strips it, and lifting is what limits that.

Protein and Calorie Cut Matter

The trials that kept muscle also made sure people ate enough protein. The 6-month trial set protein at about 0.45 gram per pound of body weight a day for every diet group, so the lifting made the difference between groups. Across 24 diet trials, higher-protein diets saved about 1 pound more lean mass than standard-protein diets. The size of the calorie cut matters too: across lifting trials, eating about 500 calories a day less than needed was enough to stop muscle gains, and the authors advise keeping the cut no bigger than that when the goal is to keep muscle. For more on protein, see our cards "Most people need more protein than the guidelines say", "Eating more protein helps you build muscle" and "You need more protein when you're losing weight".

Sources (7)

“Lifting weights while losing weight protects your muscle.”

Similar claims on Cardio & weight loss