Does eating a lot of protein make you gain fat?

Short answer

Adding protein alone did not make people fatter. Eating over 800 kcal more a day as protein left body fat unchanged. But when total calories went far over, fat still built up even on a high-protein diet.

Does eating a lot of protein make you gain fat?
'Protein has calories too → extra turns into fat' — does this formula hold?
Protein has calories too, so some say eating a lot of it will end up stored as fat. We checked what happened to body fat in studies that had people eat far more protein than usual.
307 g a day for 8 weeks
Over 800 kcal more a day, and body fat did not change
Out of 30 people, one group ate an average of 307 g of protein a day for 8 weeks (the other group ate 138 g). For a 70 kg (154 lb) person, that is about 308 g a day. They ate over 800 kcal more per day, yet body weight, body fat and lean mass (muscle and everything except fat) all stayed the same.
What about while training hard?
Body fat actually dropped by 1.7 kg
48 people did heavy strength training for 8 weeks while eating protein equal to about 238 g or 161 g a day for a 70 kg person. The high-protein group also ate more calories, but lost 1.7 kg of fat, more than the lower group (0.3 kg). Lean mass rose by 1.5 kg in both groups.
Does it hold over a full year?
Switching every 6 months, body fat did not go up
14 people switched between their usual diet and a high-protein diet, 6 months each, over 1 year. During the high-protein phase, they ate about 310 kcal more a day for a 70 kg person, from about 2,096 to 2,406 kcal, yet their body fat did not increase.
Why less fat gain?
Protein burns more and makes you eat less
21 people spent 54 hours in a room that measures calorie burn, eating as much as they wanted of a 30% or 13% protein diet. On the protein diet they burned 128 kcal more and ate 196 kcal less per day. In a study that overfed 25 people, extra calories from fat did not raise calorie burn right away, but extra protein did.
So can you eat unlimited amounts?
When total calories ran far over, fat still built up
25 people stayed in a hospital unit for 8 weeks and were fed about 40% more than usual. Body fat rose about the same whether their diet was high or low in protein. Those who ate enough protein gained lean mass. What added the fat was the extra calories, not the protein.
On a diet, protein actually helps
87 kg more fat lost, and less muscle lost
An analysis that pooled 24 studies and 1,063 people dieting on the same calories found that the high-protein groups lost 0.87 kg more fat over 12 weeks on average. They also lost 0.43 kg less lean mass.
Bottom line: calories make you fat, not protein
You can eat more protein and just watch the total
In studies that only added protein, eating hundreds of extra kcal a day did not raise body fat. Fat built up only when total calories ran far over. Eating plenty of protein works, as long as your total daily calories are not running far over.