Eating protein helps with losing fat, for a few reasons.
1. When you eat more protein, you tend to feel fuller longer.
Protein stimulates the release of satiety (stop-eating) hormones in the gut. So when you eat protein, you naturally tend to eat less, without feeling hungry.
(You can test this theory if you want. Go and try to eat an entire plain skinless chicken, or a few pounds of lean fish.)
2. Protein makes your body work to digest it.
Not all nutrients take the same energy to digest. Fat and carbohydrates are pretty easy for your body to digest and absorb, but protein takes more energy to digest and absorb.
If you eat 100 calories of protein, you’ll only use about 70 calories of it. (This thermic, or heat-producing, effect of protein is why you sometimes get the “meat sweats” after a big protein-heavy meal.)
3. Protein also helps you hang on to lean mass while you’re losing fat.
When you’re in a significant energy deficit (i.e. eating less than you burn), your body tries to throw out everything — fat, muscle, bone, hormones, etc. — all the stuff you need. It doesn’t tend to throw out just fat and keep muscle… unless you eat lots of protein.
Let’s take a deeper look: Protein, lean mass, and energy restriction
A recent study at McMaster University in Canada explored what would happen if people who were on a very low-calorie diet (about 40 percent less than normal energy needs), ate a lot of protein, and worked out hard.
For 4 weeks, a group of young men in their 20s were basically starved, but on a high-protein diet — about 2.4 g/kg.
So, for instance, a 200 lb (91 kg), relatively active young man whose energy needs would normally be 3000 calories per day might get:
- 1800 calories per day (40 percent less than normal)
- 218 grams of protein per day (2.4 x 91 kg)
This means that out of those 1800 calories per day, about 48 percent of them were from protein.
The men trained hard — lifting weights and doing high-intensity intervals 6 days a week.
After 4 weeks, on average:
- The men gained about 1.2 kg (2.6 lb) of lean body mass (LBM).
- They lost about 4.8 kg (10.5 lb) of fat.
The fact that they lost fat isn’t surprising, though that amount of fat loss in 4 weeks is pretty impressive.
What is surprising is that they gained LBM.
There was a control group, who ate more of a normal-protein, low-energy diet — about 1.2 grams of protein per kg (so, for our 200 lb / 91 kg man, that would be around 109 grams per day). This group, on average:
- Gained 0.1 kg (0.2 lb) of LBM
- Lost 3.5 kg (7.7 lb) of fat
This study was only 4 weeks long, and on a specific population group under close supervision, but it’s a cool experiment that suggests protein might be able to do some nifty things even under difficult and demanding conditions.
It’s particularly useful because it’s a randomized controlled trial. In other words, it’s not a food questionnaire where you try to remember what you ate last year — it’s a direct comparison of two similar groups whose food parameters are being closely monitored.
We don’t recommend a highly restrictive, high-protein diet combined with a Spartan-style workout plan as a long-term strategy, but if you want to try something crazy for 4 weeks, see if you can replicate these results!