Total body weight

Mean weight change in STEP 1

The scale result is substantial. I’m curious about what the total can conceal.

STEP 1 comparison

STEP 1 studied adults with overweight or obesity without diabetes. At week 68, mean body-weight change from baseline was −14.9% with semaglutide and −2.4% with placebo. These are group means from the same randomized trial.

A side-by-side picture helps me appreciate the size of the weight result without adding a second argument to it. The bars below show the reported changes in total body weight. Fat mass, lean tissue and physical function each require their own observations.

STEP 1 mean weight change at week 68: semaglutide −14.9% and placebo −2.4% — Mean body-weight change from baseline at week 68 in adults with overweight or obesity without diabetes; bar lengths show the magnitude of the decrease. Source: STEP 1.

Weight over two years

The STEP 5 trial followed adults with overweight or obesity over 104 weeks and reported sustained mean weight reduction significantly greater than placebo. Over that longer span, persistence becomes the question: does the early change endure?

Duration matters to my judgement of a weight result. So does composition. A persistent reduction in the total still leaves room to ask how fat and lean tissue changed, and whether physical ability improved alongside them. An answer tying those changes together would be more persuasive.

There is also a separate story when treatment is withdrawn. The regain trials take up that change in circumstances.

A plain platform scale standing on an olive linoleum floor beside a wooden chair — An imagined editorial still life about measuring total weight; this is not equipment documented in a trial.

Inside the lost weight

In the separate SURMOUNT-1 body-composition substudy, tirzepatide weight loss comprised roughly 75% fat mass and 25% lean mass. The proportions were similar in the placebo group. Here the percentages describe shares of the weight lost; they are not percentage changes in each tissue from its own starting amount.

I’m uneasy with treating every part of the lost weight as equally welcome. The lean component complicates my approval: the condition of the body after subtraction matters to me. These tirzepatide proportions stay with this substudy; applying them to the semaglutide trial would require additional evidence.

The physical-function findings offer another way to consider useful change. A total-weight result and a body-composition result each leave something for that question to answer.