Does replacing a meal with a protein shake help you lose weight?

Short answer

Yes. People who swapped one or two meals a day for shakes and similar meal replacements lost 1.44 kg more after 1 year than on other diets. It worked not because shakes are more filling, but because each meal had a set calorie count.

Does replacing a meal with a protein shake help you lose weight?
'One shake = fewer calories = weight loss' — does this formula hold?
Many people say a shake instead of a meal is all it takes to lose weight. We checked randomized trials where people swapped one or two meals a day for shakes, bars and similar meal replacements, looking at the effect and the reason behind it.
Results after 1 year
Meal replacement users lost 1.44 kg more
A 2019 analysis of 23 studies with 7,884 people found that those who added meal replacements to their diet lost 1.44 kg more after 1 year than those on other diets. With extra coaching support, meal replacement users lost 6.13 kg more than other diets with regular support.
Same calorie target, still a gap
The shake group lost 2.54 kg more in 3 months
Pooling 6 studies that gave both groups the same daily calorie target, people who replaced one or two meals with shakes lost 2.54 kg more in 3 months. Body weight fell 7-8% with meal replacements and 3-7% with regular food. Fewer people quit the meal replacement plan by year 1.
Why it worked: not because shakes fill you up
Liquid calories were less filling
An analysis of 253 tests from 48 papers found that eating less at the next meal to make up for an earlier snack worked best with solid or semi-solid food. When people ate more at the next meal despite the earlier snack, it was mostly after a drink.
The more you replace, the more you lose
Biggest effect at 60% or more of daily calories
An analysis of 22 studies with 1,982 people found meal replacement diets beat regular food diets with the same calories. The gap was largest when meal replacements made up 60% or more of daily calories. On 1,500 kcal a day, that is 900 kcal or more.
What about muscle?
Higher-protein shakes took off more fat
100 people used meal replacements twice a day for 12 weeks, split into higher and standard protein intake (85 finished). Weight fell 4.19 kg and 3.72 kg, with no difference, while fat fell 1.65 kg and 0.64 kg, more in the protein group. Lean mass (muscle and everything except fat) showed no difference.
Does it last? It held at 4 years
With ongoing replacements, the 8.4% loss stayed
100 people ate either regular food or replaced two meals and a snack for 3 months. Weight fell 1.5% and 7.8%. Then everyone replaced one meal and a snack for 4 years, and weight loss at 4 years was 3.2% and 8.4%.
Bottom line: a shake meal helps you lose more
The effect came from fixed calories
Swapping one or two meals for meal replacements meant 1.44 kg more weight loss at 1 year. Shakes did not fill people up more, so the effect came from each meal having a set calorie count. The products in these studies were vitamin- and mineral-fortified meal products, and the rest of the diet stayed within a set calorie target.