Does protein intake make you fat, especially after stop hitting a gym?

Question

These are just anecdotes:

• My friend's brother stopped going to the gym, and his body went fatter than before. He claimed that it's because the protein shakes.
• Another friend of mine has a housemate who is a bodybuilder. He looked good and in decent shape before the vacation. After vacation (and supposedly because of the COVID-19 situation), he looked so chubby. My friend observed he has a full carton of protein shakes too and guess the protein intakes have to do something with it.

I'm a bodybuilder as well, though I'm just into it for 2 years. Everytime I buy a new package of proteins, my friends told me the same thing: those proteins will make you fat! They sometimes told me that I'm getting fatter as well, but I believe those are just muscle gains, but I don't know. I also tend to think getting fatter is irrelevant to protein intake, but here is one valid argument by my friend:

High dietary protein intake => Increasing insulin resistance => Higher chance of diabetes type-2 => Blood sugar control failure => Increasing hunger / desire to eat.

I'm Male, 179cm, 85kg, ~17% fat (using scale tho). Now I feel insecure: does protein really make you fat? Or is it just because of the lifestyle / dietary, and are they related to protein intake as well?

Answer 1

Protein alone won't make you fat. Eating in a caloric surplus makes you fat. Calories are a combination of protein, fat, and carbs (and alcohol but hopefully that's not part of your regular diet).

So what's happened to your friends is they stopped going to the gym. So their energy expenditure went down as a result meaning the amount of daily calories they need went down. They continued eating at the rate they previously were eating meaning the amount of calories they were consuming stayed the same. As a result, they went in to a big caloric surplus and gained fat.

High dietary protein intake => Increasing insulin resistance => Higher chance of diabetes type-2 => Blood sugar control failure => Increasing hunger / desire to eat.

This is called the Insulin Model of Obesity or the Carbohydrate-Insulin Model of Obesity and it has been pretty much proven false. It doesn't look to protein as the driving force of insulin, but according to the model, insulin is the cause for weight gain so it really doesn't matter what causes it. If insulin made you fat, then the Vegan diet would be known for making you fat as most plants are typically high in carbs. Athletes who are known to eat up to 300, 400, or even 500 grams of carbs to perform would also be extraordinarily obese.

But if you want an actual study, here's a metabolic ward study that compared high carb diets to ketogenic diets. With calories the same, the subjects lost weight at the same rate regardless of diet. Now I'll admit it's hard to find studies on weight-gain, but as of what we know, insulin has very little impact on any of it.

Does Insulin cause hunger? I don't think so. Chicken and steak can cause as much insulin secretion as bread, but they're not known to cause hunger. They're much more voluminous and satiating.