Do high-protein diets change cancer risk in a clinically meaningful way?

For healthy people, does eating more protein raise or lower your cancer risk?

The short answer is: for most common cancers, total protein intake — whether high or low — does not appear to change your risk in a meaningful way. Several large meta-analyses (studies that combine results from many other studies) have looked at this question and found no significant link. For example, a meta-analysis of 13 studies on colorectal cancer found no association between high protein intake and risk (relative risk 1.006, meaning essentially no effect) [12]. Similarly, meta-analyses on ovarian cancer (10 studies), prostate cancer (12 studies), and pancreatic cancer (14 studies) all found no significant overall association [6][13][7]. Two very large Chinese cohort studies (over 133,000 people followed for 15–20 years) also found no link between total protein intake and liver cancer risk [11]. So for a healthy person, simply eating more or less protein is unlikely to meaningfully change your odds of getting these cancers.

However, the story changes when you look at the source of the protein. Dairy protein was linked to a higher risk of prostate cancer in one meta-analysis: men who consumed more than 30 grams of dairy protein per day (roughly 2.5 cups of milk or yogurt) had a 10% higher risk of prostate cancer [3]. In contrast, soy and plant proteins were linked to lower risk. A meta-analysis of 81 studies found that higher soy intake was associated with a 10% lower risk of cancer incidence overall, and each additional 25 grams of soy per day reduced risk by 4% [2]. A case-control study in Iran found that a diet high in plant protein and low in refined carbohydrates and saturated fat was linked to a 29% lower odds of breast cancer [1]. So the type of protein matters a great deal: plant-based proteins like soy appear protective, while high dairy intake may increase risk for one specific cancer.

If you already have cancer, does a high-protein diet help or hurt?

For people undergoing cancer treatment, the evidence points in a different direction: higher protein intake appears beneficial, not harmful. A study of 591 women with ovarian cancer found that those who ate more than 1 gram of protein per kilogram of body weight per day had a 31–39% lower risk of their cancer recurring compared to those eating less than 1 g/kg [8]. The same study also suggested better overall survival with higher intake of animal-based protein foods, especially dairy [8]. In breast cancer patients undergoing chemotherapy, a randomized controlled trial found that a plant-based, high-protein diet reduced fatigue from 57% to 28% (while fatigue increased in the control group), and also improved muscle mass and reduced body fat [9].

A key concern has been whether high protein might 'feed' the tumor. A rodent study using a realistic model of colon cancer and chemotherapy directly tested this: diets ranging from 8% to 32% of calories from protein had no effect on tumor growth or size [4]. The same study found that higher cumulative protein intake actually improved body weight and fat-free mass (muscle) in the animals [4]. While animal studies don't always translate to humans, this directly addresses the worry that protein might promote cancer growth — and found no evidence of that. For cancer patients, the current evidence suggests that adequate protein (at least 1 g/kg body weight) supports recovery and survival, and does not feed the tumor.

Are there special cases where high protein is risky or helpful?

Yes. Pregnancy is one situation where very high protein intake may carry a small risk. A large combined analysis of over 126,000 pregnancies from Denmark and Norway found that women who ate more than 100 grams of protein per day had a modest 10% higher risk of preterm delivery (driven by late preterm births at 34–37 weeks) [5]. However, this same study found no link to low birth weight or fetal death, and very low protein intake (below 60 g/day) was actually more harmful, raising the risk of low birth weight by 59% [5]. So the sweet spot appears to be moderate protein intake during pregnancy.

On the other end of the spectrum, a rare genetic condition called YARS1 deficiency (which impairs protein building in cells) has been treated successfully with high-protein diets and tyrosine supplementation. In a study of 9 children, 8 showed improvements in cooperation, endurance, and motor skills, and vomiting stopped in all cases [10]. This is a very specific medical use, not a general recommendation, but it shows that for some individuals, high protein can be life-changing.

About These Sources

This answer is built on 13 peer-reviewed studies — published from 2017 to 2026, 3 from 2024 or later, 8 in Q1 journals, collectively cited 193 times — selected as the most relevant from 15 studies that passed quality screening, drawn from 71 papers retrieved from a database of over 500 million.

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