We live in a protein-obsessed world. Protein shakes, high-protein meals, even everyday products in the store like bread and milk are being given a protein boost – in both their ingredients and their marketing. So how do you cut through the noise and figure out what the best sources of protein are, and why?

Protein is one of the three essential macronutrients your body needs to function correctly. The others are carbohydrates and fats. Protein is the primary building block for everything from your muscles and bones to your hair and nails. Many people also turn to high-protein diets to help with weight management – and that’s because it can give you a ‘full’ feeling and slightly boost your metabolism.

So what makes a protein source “good”? It’s not just about the number of grams on the nutrition label. Two key factors determine protein quality: its amino acid profile and its bioavailability.

Amino acids are the molecules that combine to form proteins. There are 20 different types, nine of which are “essential,” meaning your body cannot produce them on its own and must get them from food. A “complete” protein source contains all nine of these essential amino acids in adequate amounts.

Bioavailability is all about the proportion of protein from a food that gets absorbed and used by the actual cells in your body. Animal-based proteins generally have higher bioavailability than plant-based proteins because their amino acid structures are more similar to the proteins found in our bodies. However, with smart pairing, you can get all the amino acids you need from plants, too.

There are loads of protein sources available. So which offer the most significant nutritional benefits? Here’s what science has to say about it.

1. Egg Whites

While whole eggs are incredibly nutritious, if your goal is to consume the purest form of protein with the fewest calories and no fat, egg whites are the answer. The white from one large egg contains about 4 grams of protein and only 17 calories.

The Scientific Take: Egg white protein has the highest possible Protein Digestibility-Corrected Amino Acid Score (PDCAAS), which is the gold standard for measuring protein quality. A score of 1.0 shows that, after digestion, the protein provides 100% or more of the essential amino acids required by the body. This makes egg whites a kind of benchmark against which other proteins are often compared. Almost pure protein and water, this is a top choice if you’re on a strict calorie-controlled diet, or want a protein boost without adding extra fat or cholesterol.

2. Salmon

Rich in protein, bolstered by an exceptional concentration of omega-3 fatty acids, salmon is another go-to for a protein hit. A 100-gram serving of wild-caught salmon will give you around 22-25 grams of complete protein.

The Scientific Take: What sets salmon apart are the omega-3s, specifically EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These healthy fats are well-known for the cardiovascular benefits too. That’s all about reducing inflammation, lowering blood pressure, and decreasing triglycerides. Research shows the combo of high-quality protein and omega-3s in salmon makes it great at improving brain health and cognitive function. Brain fog…disappear. The protein helps build and repair tissues, while the DHA is a major structural component of the brain and retina. Eating fatty fish like salmon at least twice a week is widely recommended by health organizations, because it has a huge impact on long-term well-being.

3. Greek Yogurt

Greek yogurt is made by straining regular yogurt to remove the whey, which results in a thicker, creamier product with a much higher protein concentration. A typical 170-gram (6-ounce) serving can contain 15-20 grams of protein, roughly double that of regular yogurt.

The Scientific Take: Greek yogurt is an excellent source of casein and whey protein. Whey is a fast-digesting protein that’s great for post-workout recovery, while casein is slow-digesting, providing a steady release of amino acids over several hours. This makes Greek yogurt a great option for a filling breakfast or a satisfying snack that can keep you full for longer. Furthermore, it’s packed with probiotics—beneficial bacteria that support a healthy gut microbiome. A balanced gut has been linked to improved digestion, a stronger immune system, and even better mental health. It’s also rich in calcium, which is vital for bone health.

4. Lentils

For those following a vegetarian or vegan diet, lentils are a stand-out option. A cup of cooked lentils (about 200 grams) delivers around 18 grams of protein. While they are an “incomplete” protein on their own — meaning they are low in certain essential amino acids like methionine — this is easily solved by pairing them with a whole grain like rice.

The Scientific Take: Beyond their protein content, lentils are a nutritional powerhouse. That same cup provides a staggering 16 grams of dietary fiber, which is more than half the recommended daily intake for adults. This high fiber content aids digestion, helps stabilize blood sugar levels, and can lower cholesterol. Lentils are also loaded with folate, a B-vitamin crucial for cell growth and metabolism, and iron, which is essential for transporting oxygen in your blood. Their low glycemic index means they provide sustained energy without causing sharp spikes in blood sugar, making them an ideal food for long-lasting energy.

5. Chicken Breast

Chicken breast is a go-to for athletes and health-conscious individuals. It is one of the leanest and most concentrated sources of protein available. A single 100-gram (3.5-ounce) serving of cooked, skinless chicken breast packs a powerful punch of around 31 grams of high-quality protein, with only about 165 calories and minimal fat.

The Scientific Take: The protein in chicken breast is highly bioavailable, meaning your body can efficiently absorb and use it for muscle repair and growth. It’s a complete protein, providing all nine essential amino acids. Chicken is also a fantastic source of niacin (vitamin B3), which is crucial for converting food into energy, and selenium, a powerful antioxidant that helps protect cells from damage. Studies have consistently shown that including lean protein sources like chicken breast in your diet can support muscle mass maintenance, especially during weight loss, and promote satiety, helping to reduce overall calorie intake.

Add some high-quality protein into your diet to boost your health, manage your weight, and power-up your muscles. And use the science behind it to figure out what makes protein effective.