Can You Eat Too Much Protein? Symptoms, Side Effects, and How Much Is Too Much

By: Rachel MacPherson

The protein craze is inescapable right now but with that you've probably also heard warnings that too much protein can wreck your kidneys, cause weight gain, or somehow harm your bones. If you're trying to eat high protein to build muscle or lose fat, then you'll be relieved to know that most of these warnings are outdated or just plain wrong. 

So can you eat too much protein? Technically yes but the threshold sits a lot higher than the internet would have you believe. You might have seen all kinds of claims around what happens if you eat too much protein and what symptoms might show up, but a lot of the time these scare-mongering social media posts don't even mention what the actual limit is for healthy adults. Of course here we believe in science and what the science has to say on high-protein eating is a lot more reassuring than the myths suggest. 

How Much Protein Should You Eat in a Day?

The best, most basic advice is to try to get about 1 g of protein per lb of body weight each day, (for example, 150 g a day for a 150 lb person). This aligns with the 1.6 to 2.0 g per kg science backed recommendation that supports lean muscle and recovery from training. 

Based on your training and body composition goals you might want to adjust your protein up or down. If you lift a few times a week and just want to hold onto your muscle, then sticking closer to the lower end of that range would be just fine. If you're training hard five or six days a week and in a calorie deficit for fat loss, then bumping up to at least 1.3 g per lb gives you a nicer buffer. In a deficit you definitely want to focus on getting even more protein so you can preserve all of that hard-earned muscle mass. 

Of course you don't want to skimp out on your other macros so make sure you're getting enough carbs and fats to fuel training in daily life. Check out our guide to healthy eating for the basics. 

What Happens If You Eat Too Much Protein?

If you're eating within that normal high-protein range then not much is really going to happen. Your body will just use what it needs for muscle repair, enzymes, and hormones and then will break down the rest for energy or excrete it. Your kidneys handle the extra nitrogen without any problems as long as they're healthy. 

Now if you are trying to eat very high intakes of protein at above 3.5 g/kg or 35% of your total calories, then you might experience some digestive complaints and other issues. That's a huge amount of protein though since we're talking over 240 g a day for a 150 lb person consistently over time. 

If your extra protein pushes your total calories above what you burn, then you can definitely gain weight but that's a calorie issue rather than a protein issue. 

Too Much Protein Symptoms and Side Effects

Actual symptoms of too much protein tend to be on the mild side and mostly involve digestion. If you are overdoing it, you might notice the following:

• Gas, bloating, and changes in your stool
• Feeling overly full or losing appetite for other foods
• Increased thirst since your body uses more water to process protein
• Bad breath, especially if you are also cutting carbs

You'll probably fart more too and it's not the most fun side effect. If you're eating protein bars all day, the people around you might have some feelings about it.

Does too much protein constipate you? Not on its own. In a large population sample, there was no overall link between protein intake and constipation. What can actually trigger it is a diet very low in carbs and fiber alongside high protein, so if you're upping your protein then keep your fiber and water intake steady.

Can too much protein cause headaches? For most people, no. Some people with migraines may be more sensitive to certain high protein foods like dairy or processed meats, but this comes down to specific triggers in those foods (like sulphites or lactose) rather than the protein total.

Aside from that, symptoms like kidney pain or bone loss aren't typical in healthy adults eating within the normal high protein range. If those show up then something else is likely going on. 

Does Too Much Protein Damage Your Kidneys?

The idea that protein causes kidney damage is a long-standing one but the short answer is that it doesn't damage them in healthy people. Higher protein intake does increase your glomerular filtration rate, which is basically your kidneys working a bit harder, but dozens of controlled trials show that doesn't translate into actual kidney function decline in healthy adults.

For example, one study in exercise-trained women eating around 2.3 g/kg, which is about 1 g/lb, showed no adverse kidney or bone effects after a full year. 

If you already have chronic kidney disease or reduced kidney function, then your protein needs to be managed differently, so follow your doctor's advice rather than any generic guidance.

Will Too Much Protein Make You Gain Weight?

Eating a lot of protein on its own isn't going to cause you to gain weight if it doesn't come with the excess calories. If you keep your carbs, fats, and total calories at maintenance while eating a higher portion of your calorie limit in protein, then you won't gain weight. Weight gain comes from eating more calories than you burn and it doesn't matter what the source is. 

Protein is actually the least likely macro to end up as body fat because it has a higher thermic effect (your body uses more energy just to digest it). Plus it's very satiating. If you're tracking your intake then check out our macros guide to see how to set up your numbers properly. 

How Much Protein Is Too Much Protein?

For a healthy adult the ceiling for muscle and performance benefits is around 2 g/kg, which is roughly 1 g/lb. Above that, extra protein won't add much more muscle or strength gains but it also won't hurt you. 

At the far end of intakes, around 2.5 to 3.3 g/kg for up to a year, haven't shown clinical harm in trained adults. If you occasionally hit a big protein day, there is no need to panic. Beyond about 3.5 g/kg there's not a lot of evidence and digestive symptoms will likely become more common. For almost everyone sticking around 1 g/lb is going to get the job done. 

Takeaway 

If you're a healthy adult then getting to the point where you're eating "too much protein" is actually going to be much more difficult than what the internet suggests. The worries about kidney damage and weight gain or bone loss don't really hold up in the research so just aim for 1 g per lb of body weight and use a mix of high-quality sources. Even if you're hitting 1.25 or 1.3 g per lb, it's safe if you're training hard. 

If you want an easy way to hit your daily target, try Purist® Grass-Fed Whey Protein Isolate in a high protein shake or grab a clean protein bar for busy days. 

Rachel MacPherson is a Certified Strength and Conditioning Specialist, Certified Personal Trainer, Nutrition Coach, and health writer with over a decade of experience helping people build strength and confidence.

This article was reviewed by Rosie Borchert, NASM-CPT, for accuracy.