How protein affects the body

How protein affects the body & overall health

How does protein affect the body?

Protein plays a foundational role in nearly every system of the body, well beyond weight loss.

• Muscle. Your muscles depend on it for movement, posture and everyday activity, from climbing stairs to carrying groceries.
• Skin, hair and connective tissue. These rely on structural proteins like collagen.
• Immune system. Your body needs protein to build antibodies and immune cells that fight off illness.
• Hormones. Many hormones that regulate metabolism and digestion, including insulin and glucagon, are built from protein.

As you age, protein matters more for preserving balance, energy and independence. A position paper from the PROT-AGE group recommends at least 1.0 to 1.2 grams per kilogram a day for people over 65, and more for those who are active or managing illness. Severe kidney disease is the exception, and it may call for less.

Low protein intake can lead to fatigue, weaker immunity, slower recovery, more hunger and gradual loss of muscle. Getting enough each day is the foundation under everything else in this guide.

Protein & weight loss

How does protein help with weight loss?

When people ask how protein affects the body during weight loss, the answer often begins with one word: satiety, the feeling of being full and satisfied after eating. Protein stands out here.

Protein-rich meals stimulate hormones like PYY and GLP-1, which signal your brain that you've eaten enough. In a crossover study of 25 men, a meal with 25% of its calories from protein raised GLP-1 by 10% and PYY by 7% compared with a 14% protein meal, and hunger ratings fell by 15%. At 50% protein, GLP-1 rose 20%, PYY rose 14% and hunger fell 25%. Yet when lunch came 4 hours later, people ate about the same amount. A larger review of feeding trials reached the same conclusion: a modest fullness effect that doesn't reliably cut calories at the next meal.

These are the same hormones targeted by popular GLP-1 medications, and your body does make them naturally in response to protein-rich meals. A high-protein meal isn't a substitute for a medication, though. To learn more about how these hormones work and what foods support them, see our Ultimate Guide to the GLP-1 Diet.

PYY has an interesting backstory. One study found that high-protein meals produced the greatest PYY release and the most fullness, in people with normal weight and with obesity alike. Mice bred without PYY were resistant to protein's fullness and weight effects. That's a useful clue about the mechanism. Mice aren't people, so it isn't proof that more PYY means better weight control for you.

Protein doesn't only work on hunger. It also protects lean muscle during weight loss, and here the evidence is firmer. A 2024 systematic review of 47 randomized trials found that more protein helped prevent muscle loss in adults with overweight or obesity who were trying to lose weight, with intakes under 1.0 g/kg a day tied to a higher risk of decline. It didn't significantly protect strength or physical function. In a 2012 meta-analysis of 24 trials, higher-protein diets lasting about 12 weeks produced 0.79 kg more weight loss, 0.87 kg more fat loss and 0.43 kg more lean mass kept.

You may have heard that muscle keeps your metabolism high. It does burn more than fat at rest, about 13 calories per kilogram a day against 4.5. Run the numbers, though: 0.43 kg of muscle is only about 6 calories a day. The same 24-trial analysis found resting calorie burn fell about 142 calories a day less on higher-protein diets, with a wide margin of 16 to 269. Muscle alone doesn't explain that, so treat it as encouraging but unsettled.

Put together, protein makes weight loss feel less like a fight against your own body. If constant hunger has been the hard part, eating more of it may give you a more comfortable path forward.

Protein, metabolism & blood sugar

Does protein change how your body uses energy?

Beyond appetite, protein also influences how your body uses energy, which many people overlook when they think about weight management.

Protein can slow gastric emptying, so nutrients reach your bloodstream more steadily. In a small study of 8 people with type 2 diabetes, 55 grams of whey before a potato meal slowed emptying and produced a much smaller blood sugar rise than the same meal without whey. That's a big dose in a small group of people with diabetes, so read it as a direction, not a number you can expect for yourself.

You'll also read that high-protein diets improve metabolic flexibility, the ability to switch between burning carbs and fat. The evidence is thin. In a 12-week randomized trial of 33 older men, resistance exercise improved it, while a high-protein diet had only a limited benefit. If that's the effect you want, lift something.

The practical upside is simpler. Meals with enough protein tend to hold you longer, which makes a high-protein eating pattern easier to follow over time.

Thermic effect of protein

Does protein burn more calories during digestion?

Most people focus on how many calories they eat. Far fewer think about how many their body uses simply to process that food. This is the thermic effect of food: the energy needed to digest, absorb and metabolize nutrients.

Protein takes the most work. A review of the research puts its thermic effect at 20% to 30% of its calories, compared with 5% to 10% for carbs and 0% to 3% for fat. So 100 calories of protein costs about 20 to 30 calories to process, and that burn happens while you're digesting, not around the clock.

A 2024 systematic review and meta-analysis of 52 studies confirmed that higher-protein meals produce more of this effect than lower-protein meals of the same calories. There was a catch. In longer studies, overall daily calorie burn was higher on higher-protein diets, but the digestion effect itself no longer differed. The type of protein didn't matter either.

Protein doesn't melt fat. It gives you a small metabolic advantage that adds up modestly when you include it throughout the day, and it's a nice bonus on top of the fullness and the muscle.

How much protein you need per day

How much protein do you really need?

Most Americans know the general guideline of 46 to 56 grams a day. That's the Recommended Dietary Allowance for adult women and men. It's set to cover basic needs and prevent deficiency, and it wasn't built around muscle maintenance or weight management.

A more useful approach is to base your intake on your body weight. A practical target is 0.54 to 0.73 grams of protein per pound a day, the same as 1.2 to 1.6 g/kg. Phillips and colleagues and the 2015 review by Leidy and colleagues both land on this range, and Leidy adds at least about 25 to 30 grams per meal.

Daily protein targets at 1.2 to 1.6 g/kg

You don't need huge portions of meat. Include a solid protein source at each meal, add high-protein snacks and use convenient options like protein shakes when you need them. Our Shakez Protein Powder has 20 grams of whey protein per scoop.

Best dietary sources of protein

Where should your protein come from?

Animal proteins, like chicken, turkey, lean beef, pork, fish, seafood, eggs, Greek yogurt and cottage cheese, are highly bioavailable and contain all the essential amino acids in the proportions your body needs. They make it easy to hit a target without much volume.

Plant proteins offer their own advantages. Lentils, chickpeas, black beans, edamame, tofu, tempeh, quinoa, nuts and seeds provide protein along with fiber, antioxidants and other nutrients. Some plant foods run low in one or two amino acids, and eating a variety through the day covers it.

Protein in common foods, rounded from USDA FoodData Central

For busy days when cooking isn't realistic, our High Protein Meal Plan adds 2 extra ounces of meat per meal, about 10 more grams of protein, and ready-to-eat high-protein snacks like Protein Empanadas and Protein Peanut Butter & Jelly bring 10 to 15 grams each. Consistency drives results, so convenience counts. For a breakdown of which foods support weight management best, see our Best Foods for Weight Loss Complete Guide.

How to eat more protein every day

How do you make protein work for you?

Understanding what protein does is only useful if it fits your routine. Raising your intake doesn't require a complete diet overhaul.

Start by anchoring each meal with a protein source: eggs at breakfast, chicken or fish at lunch and a protein-rich dinner. Add Greek yogurt, cottage cheese or a handful of nuts as snacks between meals. If you're short on time, batch cook proteins on the weekend and portion them into containers. Our Complete Meal Prep Guide walks through how to do this efficiently.

If the math is the hard part, or the cooking is, that's a workload problem. Our current menu (October 2026) runs from 20 to 55 grams of protein a meal, and 20 of the 32 meals have at least 30 grams. The Nutrition Info page lists every one, so you can pick the meals that fit your number.

Make it easy withHigh Protein Meal PlanFrom $63.00View plan

The goal isn't perfection, it's consistency. Protein influences your appetite, your muscle and how you feel day to day. It isn't a quick fix. Paired with balanced meals, water and regular movement, it's one of the more reliable tools you have, and when eating feels satisfying, the habits get much easier to keep.