Can Excess Protein Turn Into Fat? What If I Eat Too Much Protein 2023?

Protein is usually heralded as the best macronutrient to help you lose weight. But does protein turn into fat if you eat too much of it?

Eating too much protein can turn into fat and make you gain weight – but it’s not as easy for your body as turning carbohydrates (carbs) or fat into fat. Read on to learn why eating too much protein turns into fat and how much you should eat to avoid gaining unwanted weight.

Does Protein Make You Fat?

Your body turns extra glucose into fat if you don’t need it. The thing is, protein isn’t usually converted to glucose – your body “prefers” carbs and fats because they’re easier to convert into calories.

If Not Energy, What Do You Need Protein For?

Proteins are long, complex molecules that your body uses to build muscle, enzymes, and other “functional” structures. 

They’re broken down in your stomach acid into amino acids or peptides (a smaller version of proteins), which are further broken down in your intestines and absorbed into the bloodstream. Your body then recombines the amino acids to make the proteins it needs.

How Does Eating More Protein Affect Body Weight?

Studies show that when resistance-trained male athletes increased their protein intake^[1] for one year, they didn’t gain fat weight – despite eating significantly more calories overall. 

Resistance-trained men didn’t even gain weight^[2] after eating more than five times the recommended amount of protein for eight weeks. This is also confirmed in female athletes^[3] – i.e., no weight gain or change in body composition.

But what if you’re a person who doesn’t exercise much and you overeat protein? The extra amino acids have to go somewhere.

What is the Immediate Fate of Excess Dietary Protein in the Body?

As stated, protein is first broken down in your stomach and intestines into amino acids. These are transported via the bloodstream to the liver and the rest of the body, where they’re primarily transformed into proteins. 

But your body can’t store amino acids. So, if you eat more than you need to build functional proteins, they’ll be made into glucose for storage as glycogen or burned for energy. 

Glucose can also be made into triglycerides and stored as fat. Some amino acids are ketogenic (i.e. leucine and lysine) and are preferentially turned into ketones^[4] – an alternative energy source to glucose.

So, amino acids from excess dietary protein can get turned into^[5] either:

• Urea, which comes out in your pee.
• Glucose (which is burned for energy, stored as glycogen).
• Fat (excess glucose is turned into triglycerides and stored as fat).
• Ketones (an alternative energy source) from ketogenic amino acids.
• Energy, made directly from amino acids.

However, using protein for energy isn’t the easiest, so your body only uses it as a last resort when there aren’t enough carbs or fats available (or you’re eating much more protein than you need for its amino acids).

Conversion to Glucose: The Last Resort

Very little glucose comes from amino acids. After eating four eggs, the participants in one study produced around 50 grams of glucose over eight hours^[6] – but only four grams (8%) came directly from the amino acids. 

So, after the person used all they needed for protein synthesis, they burned most of the excess amino acids as energy directly (measured by CO₂ production).

But this was a study using normal amounts of protein. A diet high in protein is different. If you’re overeating protein, the excess will be used as energy – around four calories of energy per gram. If you don’t need that energy right away, it’ll be stored as fat.

Does Protein Make You Gain Weight?

An increase in protein intake is usually associated with higher satiety, weight loss, and fat loss over time^[7].

But, of course, it depends on exactly what you’re eating and the type and amount of physical activity you’re doing. Plus, many high-protein foods don’t only contain protein.

High-Protein Foods Contain Carbs And Fat

Eating lots of protein means you’re probably eating more fats and carbs, too – especially if you’re eating high-fat protein sources such as meat, cheese, and other full-fat milk products. So, it can be easy to gain body weight by over-eating protein-rich foods.

Having said that, eating more protein usually leads to eating fewer calories^[8] because it’s more filling than fats or carbs. It takes longer for your stomach to digest it, hence why you feel fuller for longer after a protein-rich meal.

So, while it’s difficult to gain weight by eating more protein, it’s not impossible. At the end of the day, you need to ensure you’re not eating more calories than you’re burning through daily physical activity.

Does Excess Protein Turn Into Fat or Muscle?

Gaining body weight doesn’t necessarily mean gaining body fat. Muscle is heavier than fat, so if you’re gaining more muscle from eating more protein and exercising, you may gain weight.

Most studies don’t show an increase in body fat after eating a diet high in protein. However, some studies suggest^[9] that it can lead to weight gain – but not a bigger waist size. 

So, rather than gaining fat around your belly, you may be more likely to “bulk up” overall – probably from gaining muscle.

Risks of Consuming Too Much Protein

Most people^[10] eat much more protein than they need. There are some risks of eating too much protein, but most of the risks are due to eating too many animal sources of protein rather than plant-based sources.

Shorter Lifespan

Eating more protein instead of carbohydrates^[9] can increase your risk of all-cause death.

Conversely, a lower protein diet may be associated with living longer. Studies have found that one amino acid, particularly high in animal-based sources of protein, is associated with how long you live: methionine. 

By restricting methionine^[11] in the diet, such as by following a plant-based diet, scientists have found that you can potentially extend your lifespan^[12].

Heart Disease

Overeating red meat or dairy is linked to an increased risk of heart disease^[13]. 

However, this probably isn’t referring to the protein itself. Rather, it’s referring to the saturated fats also present in meat and dairy. So, swapping meat for plant-based sources of protein can improve heart health^[14].

Constipation

A low-fiber diet is associated with gut issues – especially constipation^[15]. Many animal-based high-protein sources are low in fiber, which you need to keep stuff moving through your gut. 

Calcium Loss

Studies suggest that eating a lot of protein can lead to calcium loss in your bones^[16]. Amino acids are acidic, so your body needs to compensate for the extra acidity by drawing alkaline minerals from your bones.

As doing lots of training also increases the acid load, high-performance athletes should consume^[17] more magnesium, potassium, and 1500 mg of calcium to counteract the effects.

What if You’re Not a “High-Performance” Athlete?

You probably don’t have to worry. Combined with exercise, protein can have a beneficial impact on bone health^[18] – especially reducing the risk of osteoporosis in postmenopausal women^[19] (without leading to weight gain)^[3].

Cancer

Studies show that eating too much meat can increase your risk of cancer and overall mortality risk. Red or processed meat is especially linked to a higher risk of colorectal cancer^[20] – one of the most common cancers of the digestive tract. 

Kidney Problems

People with kidney disease are usually told to follow a low-protein diet^[21]. That’s because when you overeat protein, your kidneys need to do more work^[22] to filter the excess amino acids into your pee. Athletes may also experience slightly reduced kidney function^[23] on a high-protein diet. 

However, studies show that a high-protein diet^[7] isn’t usually a problem for those with healthy kidney function doing a normal amount of exercise.

A weight-loss study that put healthy obese people on a high-protein diet^[24] for two years found no problems associated with kidney function or electrolyte balance.

Recommended Intake

The recommended amount of protein^[25] you should eat depends on how much physical activity you do. The more exercise you do, the more your muscles need to be repaired and the more protein you need.

Standard recommendation: 0.8 grams/kilogram body weight or 15-16% of energy intake^[26].

For athletes^[27]:

• Mildly active: 0.8-1.2 g/kg body weight.
• Very active: 1.2-1.4 g/kg body weight.
• Professional athlete^[27] or bodybuilder: 1.4-2.0 g/kg body weight.
• Some evidence exists that 3 g/kg^[27] may have beneficial effects on body composition – but only in resistance-trained athletes.

For women:

• Pregnant women: an extra 1 gram in the first trimester, nine grams during the second, and 28 grams during the third trimester.
• Breast-feeding women: an extra 19 grams/day in the first six months of lactation and 13 grams/day after that.

Your body isn’t physically able to use more than 2.0 grams of protein per kilogram^[25] (kg) of body weight (calculated for extremely active individuals), so if you exceed this, it will be used as energy rather than building proteins.

Best Sources of Protein

The best sources of protein are those that contain all nine essential amino acids. A complete protein is only found in animal products and some vegetarian sources, such as soy and hemp seeds. Other vegetarian sources can be combined to make an essential amino acid profile.

• Lean chicken
• Fish
• Lean pork
• Low-fat yogurt
• Milk 
• Parmesan cheese
• Lean beef
• Seeds (pumpkin seeds, hemp seeds)
• Nuts
• Legumes (beans, peas, and lentils)
• Eggs
• Soy and soy products (i.e. tofu)

The Bottom Line

Protein is an essential nutrient your body needs to build muscle, organs, bone, enzymes, antibodies, and other functional proteins. High-protein diets have also been shown to help boost satiety, lower overall calorie intake, and improve weight loss and body composition.

However, when it comes to the question, “does protein turn into fat?” the answer is “yes” if you eat much more protein and calories than you need. So, make sure to eat enough protein for your activity level but don’t overdo it. 

To avoid some of the negative side effects of a high-protein diet, opt for plant-based sources rather than animal sources of protein.

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