This is a Problem for Dieters
When some people decide to get lean, they make a big mistake. To reduce calories, they go low carb and low fat... at the same time.
Your body needs an energy substrate and you need to consume it. While protein can technically be transformed into energy, it's a costly and inefficient process. It needs to be turned into glucose by the liver. The problem? Once the body is efficient at turning amino acids into energy, it'll turn your stored proteins (muscle tissue) into energy more easily too.
One of the first things you learn in exercise physiology is that the energy substrate you consume the most will be used the most and used more efficiently by the body. If 60-70 percent of your caloric intake is protein, then your body will become efficient at using protein for fuel and muscle breakdown will increase over time.
The efficient energy substrates? Fats and carbs. During any diet, you want either:
- A sufficient intake of carbs: A protein and carb dominant diet (Ornish)
- A sufficient intake of fats: A protein and fat dominant diet (Keto, Atkins)
- A combination of both: A diet fairly balanced in carbs and fats (The Zone or Mediterranean)
Losing fat is an emotion-driven process. We hate what we see in the mirror and we want that fat gone now! So we tend to be overly aggressive with dieting and many will cut out both carbs and fats.
I can't tell you how many bodybuilders and figure competitors I've seen eat an 800-1200 calorie per day diet consisting of almost exclusively of protein – something like 150-250 grams of protein, 10-15 grams fat, 10-15 grams carbs per day.
I've seen some bigger bodybuilders ingest 300-400 grams of protein per day with no more than the same 10-15 grams of fat and 10-15 grams of carbs.
If you're on steroids it can work... sorta. If by "working" you mean you'll end up looking good but feeling bad. Sure, the steroids will protect their muscle mass, and they may still have energy if they take clenbuterol or ephedrine, which are essentially synthetic adrenaline or act on the same receptors as adrenaline.
But after a few weeks they feel like complete crap. Can't sleep, can't recover, no energy, mood swings, depressive symptoms, etc.
If all you consume is protein, you'll run into trouble. First, because of metabolic adaptation. What do you do when fat loss stalls? You don't have any fat or carbs to cut. All you can take out of your diet is protein. And that won't speed up the fat loss process, or if it does, it'll come with muscle loss.
And no fat intake plus no carb intake is a disaster for your hormone levels, stress management, and psychological well-being.
The Better Approach
You need a decent amount of at least one energy substrate to be functional. Keto is fine (if that's your thing) because true keto is high in fat. Same with a carnivore diet which is higher in protein than keto, but still has 40-60% of the caloric intake from fats.
The traditional low-fat bodybuilding diet is also fine because you have a good amount of carbs in there. The Zone diet, which has around 30-40% protein, 30-35% carbs and 30-35% fats is also a possible option.
You can also spend time in all three approaches and match them to the form of exercise you're doing. More details here: The 5 Biggest Fat Loss Mistakes.