For most healthy adults, consuming more than 2 grams of protein per kilogram of body weight per day crosses into excessive territory. That’s about 150 grams daily for a 165-pound person. Below that threshold, your body handles protein well. Above it, the returns diminish and the potential downsides start adding up, especially if you sustain that intake over months or years.
What the Official Guidelines Say
The Recommended Dietary Allowance for protein is 46 grams per day for adult women and 56 grams for adult men. Those numbers represent the minimum needed to meet basic nutritional needs, not an optimal target. The broader Acceptable Macronutrient Distribution Range sets protein at 10 to 35 percent of total calories for adults. On a 2,000-calorie diet, that upper end works out to about 175 grams of protein.
Mayo Clinic Health System defines excessive protein intake as anything beyond 2 grams per kilogram of body weight per day. For a 180-pound person, that ceiling is roughly 164 grams. For a 140-pound person, it’s about 127 grams. Most Americans eating a standard diet land somewhere between 60 and 100 grams daily, so hitting truly excessive levels usually requires deliberate effort through supplements or protein-focused meal plans.
What Happens When You Eat More Than You Need
Your body can only use so much protein for muscle building at one time. Research has found that about 30 grams of protein per meal is enough to maximally stimulate muscle repair and growth. Eating a larger serving in one sitting doesn’t increase that response. One study found that the benefits of protein frequency on leg muscle mass plateaued at roughly 45 grams per meal. Beyond that, the extra protein gets broken down for energy or, if total calories are in surplus, contributes to fat storage.
This doesn’t mean protein above 30 grams per meal is “wasted.” Your body still absorbs and uses it for other functions: making enzymes, supporting immune cells, maintaining skin and hair. But if your goal is building muscle, spreading your intake across three or four meals tends to be more effective than loading it all into one or two sittings.
The Kidney Question
This is the concern people raise most often, and the answer depends heavily on whether your kidneys are already healthy. High protein intake increases your kidneys’ filtration rate, essentially making them work harder to process the extra nitrogen that protein metabolism produces. Animal research shows that a high-protein diet significantly increases kidney filtration rate, blood flow to the kidneys, and even kidney weight compared to a low-protein diet.
For people with healthy kidneys, this increased workload doesn’t appear to cause damage. The kidneys adapt. But for anyone with existing kidney disease, even mild or undiagnosed, that extra filtration demand can accelerate decline. This is why high-protein diets are genuinely risky for people with compromised kidney function, and why it’s worth knowing your kidney health before committing to a very high protein intake long term.
Protein, IGF-1, and Cancer Risk
One of the more striking findings in protein research involves a growth hormone called IGF-1. Protein intake, particularly from animal sources, increases IGF-1 levels. IGF-1 helps your body grow and repair tissue, but it also appears to promote the growth of cancer cells.
A large study from the University of Southern California found that people who ate a high-protein diet during middle age (50 to 65) were four times more likely to die of cancer compared to those eating a low-protein diet. Even moderate protein intake tripled the risk. For every 10 ng/ml increase in IGF-1, people on high-protein diets were 9 percent more likely to die from cancer. Notably, these associations were strongest for animal protein. Plant-based protein sources did not carry the same risk profile.
After age 65, the relationship reversed. Higher protein intake became protective, likely because older adults need more protein to prevent muscle wasting and frailty. This age-dependent pattern suggests that the “right” amount of protein shifts across your lifespan.
Digestive Side Effects
High-protein diets often crowd out fiber-rich foods like fruits, vegetables, whole grains, and legumes. The protein itself isn’t what causes digestive problems. The issue is what it replaces. Low-fiber diets reduce stool bulk and slow transit time through your digestive system, leading to constipation, bloating, and general discomfort. If you’re eating over 150 grams of protein a day from chicken breast, protein shakes, and eggs, there may not be much room left on your plate for the 25 to 35 grams of fiber your gut needs.
Staying well hydrated also matters more on a high-protein diet, since your kidneys use extra water to flush out the byproducts of protein metabolism.
What About Athletes and Lifters
Strength athletes and serious recreational lifters are the group most likely to push protein intake well above average. The International Society of Sports Nutrition acknowledges that intakes above 3.0 grams per kilogram per day may help resistance-trained individuals lose fat mass. For a 180-pound lifter, that’s about 245 grams of protein daily.
These higher intakes have been studied in young, healthy, physically active people over relatively short time periods, and they haven’t shown kidney damage or other acute harms in that population. But 3.0 g/kg/day is far beyond what most people need. Even competitive athletes typically do well in the range of 1.6 to 2.2 grams per kilogram, which for most people falls between 110 and 180 grams per day.
Does High Protein Weaken Bones?
For years, the concern was that protein metabolism creates an acid load in the body, forcing calcium out of bones to neutralize it. This would theoretically weaken your skeleton over time. The evidence has moved decisively against this idea. While high protein intake does increase calcium excretion in urine, it simultaneously boosts calcium absorption in the gut, raises IGF-1 (which supports bone formation), and lowers parathyroid hormone (which, when elevated, breaks down bone). The net effect is neutral or positive. Multiple long-term studies have found that higher protein intake is associated with greater bone mineral density and fewer fractures, not more.
A Practical Way to Think About Limits
For a healthy adult who isn’t doing intense resistance training, 1.2 to 1.6 grams of protein per kilogram of body weight covers your needs with a comfortable margin. That translates to roughly 80 to 120 grams per day for most people. If you’re lifting heavy or trying to build muscle, going up to 2.0 g/kg is well supported. Beyond 2.0 g/kg, you’re in territory where the benefits flatten out and the potential for digestive issues, kidney stress (if you have any underlying vulnerability), and dietary imbalance grows.
The source of your protein matters too. Spreading intake across meals, favoring a mix of animal and plant sources, and keeping fiber intake high will get you more benefit from the same total grams than relying on protein shakes and processed meats alone. If you’re in middle age, paying attention to how much of your protein comes from animal sources may be especially relevant given the IGF-1 and cancer data.