Protein is having its day—or rather its decade—in the spotlight, so what happens when you eat too much?

Carolyn Williams, Ph.D., R.D.
October 28, 2020
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Credit: Shana Novak / Getty Images

Protein is a hot nutrient right now. Partly driven by the success of eating approaches like paleo and keto, protein has become the one macronutrient that people can't get enough of and are consistently looking for ways to get more over the past 10 years. Protein is perceived to do little harm; in fact, most worry more about not getting enough.

Consuming adequate protein, meaning an intake of around the RDA (about 46-56 grams per day) or even a little above it, is essential for strength and lean body mass, as well as immune health, gut health, and bone health (learn more about how much protein you should aim for every day). But like everything else, moderation is still key. Consistently consuming protein amounts that greatly exceed one's needs has side effects. Some of these are some mild, short-term effects; other are more long-term and largely dependent on what type of protein sources you're going overboard in consuming.

Check out these 8 things that can happen to your body when you eat too much protein.

1. Dehydration & Increased Thirst

Unlike carbs and fat, protein contains nitrogen which must be removed and turned into urea before the body can use a protein's amino acids. The kidneys filter urea from the blood and remove it from the body as urine. This means higher protein intake requires more water or fluid to help the kidneys do their job. And if fluid intake doesn't keep up with the kidney's needs, the hypothalamus will trigger your thirst response to encourage you to consume some fluids. (Learn more about 10 side effects of not drinking enough water.)

2. Constipation

Increasing protein means adding protein-rich food and supplements, and sometimes adding those protein foods in place of lower-protein, higher-carb ones such as fruit, grains, legumes, and some vegetables. These changes can drastically decrease fiber intake, and constipation is common when following higher-protein, lower-carb diets due to this decrease in fiber, as well as increased fluid needs. To avoid this, aim to get 25 to 30g of fiber each day, and increase fluid intake to account for increased protein. (Eat more of these high-fiber foods to help you poop.)

3. Weight May Go Up or Down

Consuming adequate protein is essential when trying to lose weight. In fact, research suggests that higher-protein diets may even be more effective due to protein's effects on metabolism and satiety. This can work well if calorie intake isn't exceeding needs. But if calories exceed that, then that extra energy is stored as fat—including calories from protein. Additionally, higher-fat protein foods such as some animal proteins and dairy products will also be higher in calories due to their fat content.

4. Bad Breath

Lower-carb diets like Atkins and keto require replacing carb calories by bumping up protein and fat intakes to get enough energy, with the goal being to put the body into ketosis, and bad breath or "keto breath" is a side effect of ketosis (learn more about the not-so-sexy side effects of keto). The changes are due to a build-up of keto acids, a by-product created when the body breaks down fat, and toothbrushing doesn't help this type of breath issue much. It's a lack of carbs that triggers ketosis and its' associated breath, which means higher protein isn't the direct cause but rather a contributing player.

5. Increased Risk for and Frequency of Gout

Certain meat and seafood proteins increase risk for gout, an inflammatory type of arthritis that usually occurs in the feet and toes. Gout is caused by crystals that form due to a build-up of uric acid, a by-product created when the body breaks down purines. Normally, the acid is excreted in urine, but in some individuals, it builds up leading to gout. The key to preventing this is to limit foods with purines and animal proteins like organ meats, as well as certain seafood like shellfish, sardines, and tuna, are major sources of purines.

6. Increased Cancer Risk

Higher-than-needed protein intakes that regularly consists of processed meats and higher-fat red meats can increase your cancer risk. Processed meats appear to pose the greatest threat. In fact, research suggests that colorectal cancer risk increases by 18% when 50g of processed meats (approximately one hotdog or 4 pieces of bacon) is eaten daily. To lower risk, limit processed and red meats by focusing on other proteins like seafood, lean poultry, legumes, nuts and seeds, and whole grains (add these 6 cancer-fighting foods to your diet.)

7. Change in Heart Disease Risk

Higher protein intakes can increase heart disease risk, but it depends on the protein source and what else is in the protein (such as saturated fat or fiber). When increasing protein intake means eating more higher-fat animal protein with saturated fat, this eating pattern increases risk. But when eating more protein means consuming more legumes, seafood, lean animal proteins, and nuts and seeds, risk doesn't really increase. In fact, eating more protein by consuming foods like these actually decreases risk as most studies suggest that following a lower-carb diet with protein-rich foods is associated with lower total LDL and total cholesterol, lower blood pressure, and higher HDL. (Try eating more of these top 15 foods for heart health.)

8. Increased Susceptibility to Kidney Stones

Higher protein intakes increase the kidneys' workload, and this is an important reason why those with kidney disease shouldn't consume higher amounts of protein. But for healthy individuals, higher protein intakes don't appear to impact overall kidney function. However, it can increase risk for kidney stones which form as a result of uric acid build-up, as well as a lack of calcium or fluid. Reduce risk by minimizing the same purine-rich protein food mentioned in above, and getting adequate calcium and fluid each day.

Carolyn Williams, PhD, RD, is author to the new cookbook, Meals That Heal: 100 Everyday Anti-Inflammatory Recipes in 30 Minutes or Less, and a culinary nutrition expert known for ability to simplify food and nutrition information. She received a 2017 James Beard Journalism award, and her work is regularly featured in or on respective websites for Cooking Light, RealSimple, Parents, Health, EatingWell, Allrecipes, My Fitness Pal, eMeals, Rally Health, and the American Heart Association. You can follower on Instagram @realfoodreallife_rd or on carolynwilliamsrd.com.