Of the three macronutrients — protein, carbohydrates and fat — protein has a pretty stellar reputation. And hey, proteins aren't called the "building blocks of life" for nothing. You need them in your diet to make and repair your cells, per the U.S. National Library of Medicine.
Luckily, being deficient in protein is almost unheard of in the United States, according to the Physicians Committee for Responsible Medicine.
David Buchin, MD, director of bariatric surgery at Huntington Hospital and founder of Long Island Obesity Surgery, says most adults need just 40 to 50 grams per day. According to a 2015-2016 survey from the USDA, though, people assigned male at birth eat an average of 97 grams per day while those assigned female at birth get 69 grams.
But there can be too much of a good thing. Eating too much protein (more on what constitutes too much in a minute) can lead to a few unpleasant side effects.
Here are five signs there's too much protein in your diet.
1. You’re Dehydrated
Even if your water intake hasn't changed at all, you could feel dehydrated as a result of eating a diet rich in meat, eggs, Greek yogurt and other high-protein foods, says Alicia Galvin, RD, LD, resident dietitian for Sovereign Laboratories.
The most likely reason is that a high-protein diet could lead to elevated nitrogen levels, per the Mayo Clinic. "One of the components of protein is nitrogen," Galvin explains. "And if you're eating too much protein, the body will try to flush out that extra nitrogen, which will lead to flushing out water and increasing urination."
That can lead to dehydration, says Dr. Buchin, whose bariatric patients mostly follow a high-protein diet. "You become dehydrated because you're losing a lot of water when you urinate all that nitrogen out," he says.
2. You’ve Got a Headache and You Feel Weak
Headaches and general fatigue are two other potential side effects that can set in if you're dehydrated from eating too much protein, Galvin says.
These symptoms also can come about as a result of the body being in ketosis, Dr. Buchin says. "When you're on a mostly protein diet, you are ketonic," he says.
"You feel weak because you don't have a lot of sugar in your body," Dr. Buchin says. "You feel really tired because there really is no sugar left. You've burned all of your sugar stores."
3. Your Breath Stinks
On your high-protein shopping list: chicken, almonds, eggs — and breath mints? It may be a good idea, because many people report dealing with nasty breath as a result of a high-protein diet.
The scent is pretty unmistakeable, too: "It smells like rotten fruit," Dr. Buchin says.
That's likely because a body in ketosis can produce acetone, the same ingredient found in nail polish remover. The presence of the ketone acetone in the breath can even be an indicator that a person is in ketosis, per a small April 2015 study in Nutrition Journal.
Galvin says that two amino acids found in protein may also be to blame. "It could be because two of the amino acids that are used in the mouth and by the bacteria to make the bad breath are these sulfur-containing amino acids: cysteine and methionine," Galvin says. "So when people consume protein, they have certain types of bacteria that are going to convert amino acids into those sulfur compounds, and that can lead to bad breath."
4. You Feel Constipated
If you're eating a lot of protein, chances are you're cutting back in another area of your diet. Take a popular high-protein diet like Atkins, for instance. It calls for eating lots of protein and severely restricting carbs. Per the Mayo Clinic, that means you could be missing out on fiber, which can lead to constipation.
People assigned female at birth should be getting 21 to 25 grams of fiber per day, while those assigned male at birth should get 30 to 38 grams daily, according to the Mayo Clinic. Eating fiber-rich foods, such as whole grains and legumes, can bulk up your stool as well as soften it, which helps prevent and relieve constipation.
Constipation could also happen when you add proteins back into your diet — for example, vegetarians and vegans who begin eating protein-rich meat again, Galvin says.
5. You’re Dealing with Kidney Stones
For most people, the symptoms above aren't a huge deal. But if you have kidney issues, eating too much protein could be something to worry about.
"The biggest thing is long-term, kidney damage from having very high protein for an extended period of time," Galvin says.
There are a few reasons why. Eating too much animal protein — as in meat, eggs and seafood — could increase your body's levels of uric acid, which could then lead to the development of kidney stones, per Harvard Health Publishing. A high-protein diet also decreases the body's levels of urinary citrate, which is a chemical that keeps kidney stones from forming.
Plus, eating a lot of protein tells the body to excrete calcium, which may also lead to the formation of kidney stones, according to the National Kidney Foundation.
How Much Protein Is Too Much?
Unfortunately, there isn't a straightforward answer to how much protein you should eat per day, because it depends on a person's age, body weight and lifestyle.
"Generally, the rule of thumb is 0.8 grams of protein per kilogram of body weight," Galvin says. "With that, you'll be hitting most of your needs."
Keep in mind that 1 kilogram equals 2.2 pounds. So, for example, a 140-pound person should eat about 51 grams of protein each day. But some people will need more.
"If you're very physically active or you're an athlete or you're working out on a regular basis, that'll increase to 1.2 to 1.7 grams of protein per kilogram," Galvin says. "Sometimes it's even higher, like if someone's a professional athlete. There's a range."
How high you can go safely is a different story, and there's no agreed-upon limit. "It's very dependent on the size of the patient, how much exercise that person is doing and how much muscle mass that person has," Dr. Buchin says.
A review from March 2016 in Food & Function concluded it's OK to eat 1 gram of protein per pound of body weight per day. In the example of the 140-pound person, then, that'd be 140 grams of protein in a day.
Harvard Health Publishing puts the limit at 2 grams per kilogram of body weight, which is 125 grams per day for that 140-pound person. But taking in more than that shouldn't become a habit. That much protein over time can lead to digestive, kidney and blood health issues, according to the Food & Function review.
When you take your whole diet into account, no more than 35 percent of your daily calories should come from protein, per the U.S. National Library of Medicine.
The good news is that most of the symptoms covered above will clear up as soon as you reduce your protein and eat more carbohydrates. "Drink some Gatorade," Dr. Buchin says. "That will give you more energy and will make you feel a lot better and stop that ketosis process."
Is This an Emergency?
- U.S. Department of Agriculture (USDA): "What foods are in the Protein Foods Group?"
- Physicians Committee for Responsible Medicine: "Protein"
- USDA: "Protein Intake of Adults"
- UChicago Medicine: "Ketogenic diet: What are the risks?"
- Nutrition Journal: "Acetone as Biomarker for Ketosis Buildup Capability - A Study in Healthy Individuals Under Combined High Fat and Starvation Diets"
- Mayo Clinic: "Are High-Protein Diets Safe for Weight Loss?"
- Mayo Clinic: "Dietary Fiber: Essential for a Healthy Diet"
- Harvard Health Publishing: "5 Steps for Preventing Kidney Stones"
- National Kidney Foundation: Kidney Stone Diet Plan and Prevention
- Food & Function: "Dietary Protein Intake and Human Health"
- Harvard Health Publishing: "When It Comes to Protein, How Much is Too Much?"
- U.S. National Library of Medicine: "Protein in Diet"