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Proteins are the main building blocks of your body, used to make muscles, tendons, organs and skin, as well as enzymes, hormones, neurotransmitters and various tiny molecules that serve many important functions.

Without protein, life as you know it would not be possible.

Proteins are made out of smaller molecules called amino acids, which are linked together like beads on a string. These linked amino acids form long protein chains, which are then folded into complex shapes.

Some of these amino acids can be produced by your body, while you must get others through your diet. The latter are called essential amino acids.

Protein is not just about quantity but also quality.

Generally speaking, animal protein provides all essential amino acids in the right ratio for you to make full use of them — which makes sense, as animal tissues are similar to your own tissues.

If you’re eating animal products like meat, fish, eggs, or dairy every day, you’re likely doing pretty well protein-wise already.

However, if you don’t eat animal foods, getting all the protein and essential amino acids your body needs is a bit more challenging. In this case, you may be interested in this article on the 17 best protein sources for vegans.

Few people really need protein supplements, but they can be useful for athletes and bodybuilders.

Summary Protein is a structural molecule assembled out of amino acids, many of which your body can’t produce on its own. Animal foods are usually high in protein, providing all essential amino acids.

Protein is incredibly important when it comes to losing weight.

As you know, you need to take in fewer calories than you burn to lose weight.

It’s well supported by science that eating protein can increase the number of calories you burn by boosting your metabolic rate (calories out) and reducing your appetite (calories in) (1).

Protein at around 25–30% of total daily calories has been shown to boost metabolism by up to 80–100 calories per day, compared to lower protein diets (2, 3, 4).

Yet, probably the most important contribution of protein to weight loss is its ability to reduce appetite and cause a spontaneous reduction in calorie intake. Protein keeps you feeling full much better than both fat and carbs (5, 6).

One study in obese men showed that protein at 25% of calories increased feelings of fullness, reduced the desire for late-night snacking by half and reduced obsessive thoughts about food by 60% (7).

In another study, women who increased their protein intake to 30% of calories ended up eating 441 fewer calories per day and lost 11 pounds in 12 weeks — simply by adding more protein to their diet (8).

But protein not only helps you lose weight, it can also prevent you from gaining weight in the first place.

In one study, a modest increase in protein from 15% to 18% of calories reduced the amount of fat people regained after weight loss by 50% (9).

A high protein intake also helps you build and preserve muscle mass, which burns a small number of calories around the clock.

Eating more protein makes it much easier to stick to any weight loss diet — be it high-carb, low-carb or something in between.

According to these studies, a protein intake of around 30% of calories may be optimal for weight loss. This amounts to 150 grams per day for someone on a 2000-calorie diet.

You can calculate it by multiplying your calorie intake by 0.075.

Summary A protein intake at around 30% of calories seems to be optimal for weight loss. It boosts your metabolic rate and causes a spontaneous reduction in calorie intake.

Muscles are largely made of protein.

As with most tissues in your body, muscles are dynamic and constantly being broken down and rebuilt.

To gain muscle, your body must synthesize more muscle protein than it breaks down.

In other words, there needs to be a net positive protein balance in your body — often called nitrogen balance, as protein is high in nitrogen.

For this reason, people who want a lot of muscle need to eat a greater amount of protein (and lift weights, of course). It’s well documented that a higher protein intake helps build muscle and strength (10).

People who want to hold on to muscle they’ve already built may need to increase their protein intake when losing body fat, as a high protein intake can help prevent muscle loss that usually occurs when dieting (11, 12).

When it comes to muscle mass, studies usually don’t look at the percentage of calories but rather daily grams of protein per kilograms or pounds of body weight.

A common recommendation for gaining muscle is 1 gram of protein per pound of body weight, or 2.2 grams of protein per kg.

Other scientists have estimated the protein needs to be a minimum of 0.7 grams per pound, or 1.6 grams per kg (13).

Numerous studies have tried to determine the optimal amount of protein for muscle gain but many reach different conclusions.

Some studies show that more than 0.8 grams per pound (1.8 grams per kg) have no benefit, while others indicate that intakes slightly higher than 1 gram of protein per pound (2.2 grams per kg) is best (14, 15).

Though it’s hard to give exact figures due to conflicting study results, about 0.7–1 grams per pound (1.6–2.2 grams per kg) of body weight seems to be a reasonable estimate.

If you’re carrying a lot of body fat, using either your lean mass or your goal weight, instead of your total body weight, is a good idea, as it’s mostly your lean mass that determines the amount of protein you need.

Summary It’s important to eat enough protein if you want to gain and/or maintain muscle. Most studies suggest that 0.7–1 grams per pound of lean mass (1.6–2.2 grams per kg) are sufficient.

Disregarding muscle mass and physique goals, people who are physically active do need more protein than people who are sedentary.

If your job is physically demanding, you walk a lot, run, swim or do any sort of exercise, you need to eat more protein.

Endurance athletes also need significant amounts of protein — about 0.5–0.65 grams per pound, or 1.2–1.4 grams per kg (16, 17).

Older adults have significantly increased protein needs as well — up to 50% higher than the DRI, or about 0.45–0.6 grams per pound (1–1.3 grams per kg) of body weight (18, 19).

This can help prevent osteoporosis and sarcopenia (reduction in muscle mass), both significant problems in the elderly.

People recovering from injuries may also need more protein (20).

Summary Protein requirements are significantly increased in people who are physically active, as well as in older adults and people recovering from injuries.

Does Protein Have any Negative Health Effects?

Protein has been unfairly blamed for a number of health problems.

Some people believe that a high-protein diet can cause kidney damage and osteoporosis.

However, these claims are not supported by science.

Though protein restriction is helpful for people with pre-existing kidney problems, protein has never been shown to cause kidney damage in healthy people (21, 22).

In fact, a higher protein intake has been found to lower blood pressure and help fight diabetes, which are two of the main risk factors for kidney disease (23, 24).

Any assumed detrimental effects of protein on kidney function are outweighed by its positive effects on these risk factors.

Protein has also been blamed for osteoporosis, which seems strange considering that studies show that it can, in fact, prevent this condition (25, 26).

Overall, there is no evidence that a reasonably high protein intake has any adverse effects in healthy people trying to stay healthy.

Summary Protein does not have any negative effects on kidney function in healthy people and studies show that it leads to improved bone health.

The best sources of protein are meats, fish, eggs and dairy products, as they have all the essential amino acids that your body needs.

Some plants are fairly high in protein as well, such as quinoa, legumes and nuts.

However, most people generally don’t need to track their protein intake.

If you’re a healthy person trying to stay healthy, then simply eating quality protein with most of your meals, along with nutritious plant foods should bring your intake to an optimal range.

This is a very common misunderstanding.

In nutrition science, “grams of protein” refers to grams of the macronutrient protein, not grams of a protein-containing food like meat or eggs.

An 8-ounce serving of beef weighs 226 grams but only contains 61 grams of actual protein. Similarly, a large egg weighs 46 grams but only packs 6 grams of protein.

If you’re at a healthy weight, don’t lift weights and don’t exercise much, then aiming for 0.36–0.6 grams per pound (0.8–1.3 gram per kg) is a reasonable estimate.

This amounts to:

• 56–91 grams per day for the average male.
• 46–75 grams per day for the average female.

But given that there is no evidence of harm and a significant evidence of benefit, it’s likely better for most people to err on the side of more protein rather than less.