What are the risks of a high-protein diet?

What are the risks of a high protein diet? For most healthy people eating 0.8 to 1.6 grams of protein per kilogram of body weight per day, the answer is basically none. Your body needs protein to build muscle, repair tissue, and keep your immune system working. The problems start when you eat way more protein than your body can use, or when you already have a health condition that makes extra protein a bad idea.

Research published in Food and Function found that long term consumption of protein at 2 grams per kilogram of body weight per day is safe for healthy adults. The study also noted that going above 2 grams per kilogram per day for extended periods may lead to digestive, renal, and vascular abnormalities.

So where exactly do the risks come in? Let’s break down what the science actually says.

Can too much protein damage your kidneys?

For healthy people with normal kidney function, eating extra protein does not cause kidney damage. A 2024 meta analysis published in Frontiers in Nutrition looked at the connection between dietary protein intake and chronic kidney disease risk. The researchers found that higher protein intake from total, plant, or animal sources was actually associated with lower CKD risk in healthy populations.

The story changes if you already have kidney problems. Research from the Journal of the American Society of Nephrology shows that high protein intake causes your kidneys to work harder by increasing something called glomerular hyperfiltration. This means your kidneys filter blood at a faster rate than normal. For healthy kidneys, this extra work is fine and your body adapts. For kidneys that are already damaged or struggling, this added strain can speed up decline.

The World Health Organization and kidney disease guidelines recommend people with existing CKD eat around 0.8 grams of protein per kilogram of body weight per day. People on dialysis actually need more protein, not less.

Here is the bottom line on kidneys. If your kidneys work normally, high protein diets appear safe based on current evidence. If you have diabetes, obesity, hypertension, or a family history of kidney disease, talk to your doctor before loading up on protein. These conditions put you at higher risk for kidney problems.

Does eating lots of protein cause constipation?

Yes, high protein diets commonly lead to constipation, but protein itself is not the problem. The real issue is what you stop eating when you focus heavily on protein.

Animal proteins like chicken, beef, fish, and eggs contain zero fiber. When these foods take up most of your plate, fiber rich foods like vegetables, fruits, and whole grains get pushed aside. Your digestive system needs fiber to keep things moving. Without it, stool becomes hard and difficult to pass.

Research shows that high protein, low carbohydrate diets reduce fiber intake significantly because carbohydrates are the main source of dietary fiber. Most adults need 25 to 30 grams of fiber daily, but people eating protein heavy diets often fall way below this number.

The fix is simple. Keep eating protein, but add fiber rich foods to every meal. A side of vegetables with your steak, some berries with your Greek yogurt, or beans mixed into your chicken salad all work. You do not have to choose between protein and fiber.

Will high protein diets make you dehydrated?

They can if you do not drink enough water. When your body breaks down protein, it produces waste products like urea that your kidneys need to flush out. This process requires water. Research shows that high protein intake increases the body’s production of these waste products, which means you need more fluids to process everything.

One small study found that people eating 3.6 grams of protein per kilogram per day showed worse hydration status compared to those eating moderate amounts. That level of protein intake is extreme and well above what most people eat, but the principle holds at lower levels too.

If you eat a lot of protein, drink more water than you normally would. Aim for at least 2 to 3 litres per day, more if you exercise regularly or live in a hot climate.

Does protein leach calcium from your bones?

This used to be a big concern. The theory said that digesting protein creates acid in your body, and your bones release calcium to neutralize that acid. More protein, more acid, more calcium lost from bones.

Recent research has flipped this idea on its head. A 2025 study published in Scientific Reports using data from over 16,000 participants found a positive association between protein intake and bone mineral density. Higher protein intake was linked to stronger, not weaker, bones.

The International Osteoporosis Foundation and European Society for Clinical and Economical Aspects of Osteoporosis now state that higher protein diets benefit bone health and help reduce hip fracture risk, as long as calcium intake stays adequate.

What explains the turnaround? Protein increases intestinal calcium absorption, stimulates release of IGF 1 which helps build bone, and supports muscle mass which protects bones from fractures. The old acid ash hypothesis did not account for these benefits.

The current research suggests that protein helps bones when you also get enough calcium and vitamin D. A meta analysis from Wallace and Frankenfeld showed that protein intake above the recommended dietary allowance reduced hip fracture risk.

What happens if you eat way too much protein?

Eating more than 2 grams of protein per kilogram of body weight per day for long periods may cause problems. The research on this is not completely settled, but studies have noted these potential issues.

1. Digestive discomfort including bloating, gas, and irregular bowel movements
2. Increased workload on kidneys to process nitrogen waste
3. Possible links to heart disease when protein comes mainly from red and processed meats
4. Nutrient imbalances from crowding out other food groups

A 2016 review in Food and Function put the tolerable upper limit at 3.5 grams per kilogram per day for well adapted subjects, meaning people who have gradually increased their intake over time. For context, this would be about 280 grams of protein daily for an 80 kilogram person. That is extremely high and difficult to reach through normal eating.

How much protein is actually safe?

Here are the numbers backed by research.

1. The recommended dietary allowance to prevent deficiency is 0.8 grams per kilogram of body weight per day for sedentary adults
2. Active people who exercise regularly need about 1.1 to 1.5 grams per kilogram per day
3. People who lift weights or train for endurance events need 1.2 to 1.7 grams per kilogram per day
4. Adults over 40 to 50 years old benefit from 1 to 1.2 grams per kilogram per day to prevent muscle loss
5. Research shows that long term consumption up to 2 grams per kilogram per day is safe for healthy adults
6. Going above 2 grams per kilogram per day chronically may lead to health issues

For a 70 kilogram person, these ranges work out to about 56 grams per day at the low end, up to 140 grams per day for highly active individuals, with 2 grams per kilogram being the upper safe limit at 140 grams daily.

The Mayo Clinic recommends keeping protein intake to no more than 2 grams per kilogram of ideal body weight if you want to follow a high protein diet.

Does the type of protein matter for health risks?

Yes. Research from several studies shows that animal protein, especially from red and processed meats, carries higher risks than plant based protein or fish.

The Singapore Chinese Health Study found that animal protein was associated with increased risk of end stage kidney disease compared to plant protein. Possible reasons include the acid load from animal protein, higher phosphate content, and effects on gut bacteria that cause inflammation.

Fish and seafood stand out as healthier options. A 2017 study showed that soy and fish consumption as protein sources was linked to better cardiovascular health.

Plant proteins from legumes, nuts, and tofu come with fiber and tend to have lower saturated fat content. Switching some animal protein for plant protein reduces risk while still meeting your protein needs.

Who should be careful with high protein diets?

Some groups face higher risks from eating lots of protein.

1. People with existing kidney disease or reduced kidney function
2. People with diabetes, as they face higher risk of kidney complications
3. People with a family history of kidney problems
4. People taking certain medications that affect kidney function
5. People who do not drink enough water

If you fall into any of these categories, work with a doctor or dietitian before increasing your protein intake significantly.

FAQ

Can high protein diets cause bad breath?

Yes. When your body breaks down protein, it produces ammonia as a byproduct. Some people notice a metallic or ammonia like smell to their breath when eating very high protein diets, especially if carbohydrate intake is low. This is common on ketogenic diets where protein is high and carbs are very low.

Do high protein diets increase heart disease risk?

It depends on your protein sources. Diets high in red and processed meats raise cholesterol levels and heart disease risk. Diets high in fish, poultry, legumes, and nuts do not show this increased risk. Choose lean proteins and include fish two to three times per week for heart health.

Should older adults eat more or less protein?

More. Adults over 65 need about 1 to 1.2 grams per kilogram of body weight daily to prevent muscle loss and maintain strength. Research shows older adults benefit from higher protein intake to preserve mobility and reduce fracture risk.

Is protein powder safe?

Protein powder itself is safe for most people. Problems arise when protein powder replaces whole foods, reducing your intake of fiber, vitamins, and minerals. Some powders contain lactose which causes digestive issues for lactose intolerant people. Others contain artificial sweeteners that may affect gut health. Check labels and use protein powder as a supplement to a balanced diet, not a replacement.

How do I know if I am eating too much protein?

Watch for these signs. Persistent constipation, dehydration despite drinking water, bad breath, fatigue, and unexplained weight gain. If your protein intake exceeds 2 grams per kilogram of body weight daily for extended periods, consider reducing it.

Can vegetarians get enough protein safely?

Absolutely. Legumes, tofu, tempeh, nuts, seeds, and whole grains all provide protein. A cup of lentils has about 18 grams, a cup of tofu has about 20 grams, and a cup of quinoa has about 8 grams. Vegetarians who eat varied diets meet their protein needs without the risks associated with high red meat consumption.

Balancing protein intake is especially important for anyone managing their weight through diet and exercise — if you’re just getting started, our guide on how an obese person should start exercising covers how to pair nutrition with safe, progressive movement. For a personalised nutrition and training plan that accounts for your individual health needs, work with a personal trainer in Port Melbourne who can guide you every step of the way.