Can You Eat Too Much Protein? Recommended Intakes by Age and What Research Shows

Is more protein always better for your body?

Protein is an essential nutrient that forms the basis of muscles, skin, hair, blood, enzymes, and more. Recently, information encouraging people to “make sure they get enough protein” has become increasingly common. As a result, many people may believe that the more protein they consume, the better it is for their health.

However, research on aging and lifespan is revealing a slightly different picture. Protein deficiency can weaken the body. On the other hand, some studies have linked excessive protein intake during middle age to higher rates of disease and death. And that relationship may even reverse depending on age.

The conclusions of this article are as follows:

• Both excessive and inadequate protein intake are thought to be undesirable.
• The key considerations differ for middle-aged and older adults.

How much should you eat daily? Recommended amounts by age

In Japan, the Ministry of Health, Labour and Welfare sets recommended amounts for each nutrient in the “Dietary Reference Intakes for Japanese.” The 2025 protein standards are as follows:

The “recommended amount” is the amount needed to prevent deficiency in most people. The “target amount” indicates the desirable percentage of total energy (calories) to obtain from protein, with factors such as the prevention of lifestyle-related diseases in mind.

Two points here deserve attention.

First, the upper limit for the target amount is 20% for all age groups. Although the standards state that there is not yet sufficient evidence regarding the effects of excessive intake on the body, the upper limit is set at 20% in consideration of potential effects on metabolism and the health of older adults.

Second, the lower limit increases with age. It is 14% for ages 50–64 and 15% for ages 65 and older. This is because ensuring that older adults do not have insufficient protein becomes increasingly important.

For example, for someone who consumes 2,000 kcal daily, 15% of their energy intake is 300 kcal. Since protein provides approximately 4 kcal per gram, this equals about 75 g. A range of 13–20% corresponds to approximately 65–100 g.

Does excessive intake increase disease risk? An 18-year study in the United States

One well-known study has examined the relationship between protein and lifespan. It was published in 2014 by a research group from the University of Southern California and other institutions [1].

In this study, researchers examined the diets of 6,381 Americans aged 50 or older who participated in the National Health and Nutrition Examination Survey and then followed them for approximately 18 years to monitor mortality. Participants were divided into three groups based on the percentage of their daily energy intake from protein.

• Low-protein group: Less than 10%
• Medium-protein group: 10–19%
• High-protein group: 20% or more

The results differed significantly by age.

For those aged 50–65, the high-protein group had approximately 1.7 times the risk of overall death (reported as a “75% increase” in the study abstract) and approximately 4.3 times the risk of death from cancer compared to the low-protein group. The medium-protein group also had approximately 3 times the risk of death from cancer.

For those aged 66 and older, the results were the opposite. The high-protein group had approximately 30% lower risk of overall death and approximately 60% lower risk of death from cancer compared to the low-protein group.

In addition, the risk of death from diabetes tended to be higher for those who consumed more protein at any age. However, the number of people who died from diabetes was very small, and the figures varied widely. This section requires particularly careful interpretation.

Furthermore, there were differences depending on whether the protein came from animal sources, such as meat and dairy, or plant sources, such as beans. The study abstract reported that these associations either disappeared or weakened when the protein was plant-based.

The research group focused on a hormone called “IGF-1,” which is involved in growth and cell proliferation. The idea is that consuming more protein increases IGF-1, which may in turn contribute to cancer growth.

What have animal studies revealed?

Studies using mice have also examined the relationship between protein and lifespan.

A research group at the University of Sydney in Australia prepared 25 types of feed with varying ratios of protein, carbohydrates, and fats and allowed 858 mice to eat as much as they liked [2]. As a result, mice fed the lowest-protein, highest-carbohydrate diet had the longest lifespan and the best metabolic health. Mice fed a high-protein, low-carbohydrate diet did not live longer, even though they ate less and consumed fewer calories.

In addition, a research group at the University of Washington in the United States reported that mice fed a high-protein diet were more prone to developing atherosclerosis [3]. It is thought that consuming protein increases amino acids in the blood, which may cause the “mTOR” switch in immune cells (macrophages) in the blood vessel walls to become overactive.

However, these are results from mice. What happens in mice may not necessarily happen in humans.

Why do the considerations differ for middle-aged and older adults?

In the earlier American study, the results were opposite for those aged 50–65 and those aged 66 and older. This is thought to be because the body’s needs change with age.

Middle age is a period when most people still maintain their muscle mass and weight. It has been suggested that continuing to consume large amounts of protein during this period may cause “growth switches” such as IGF-1 and mTOR to become overactive, which may be linked to diseases such as cancer.

On the other hand, as people age, they tend to eat less overall. Muscle mass also decreases with age. A condition in which muscle mass and strength decline is called “sarcopenia,” while a state in which physical and mental strength weakens and a person approaches the need for nursing care is called “frailty.” For older adults, inadequate protein intake tends to be more problematic than excessive intake.

In fact, a study that followed 2,066 Americans aged 70–79 for three years reported that the group with the highest protein intake lost approximately 40% less “fat-free body mass,” such as muscle mass, compared to the group with the lowest intake [4]. This was also an observational study, so it cannot be concluded that protein alone was the cause. Nevertheless, it is one of the results indicating that inadequate intake after age 65 requires attention.

The dietary reference standards also raise the lower limit to 15% for those aged 65 and older. However, they state that it is still difficult to clearly determine the amount needed to prevent frailty [5].

Is excessive intake harmful to the kidneys?

You may have heard that “excessive protein intake puts a strain on the kidneys.” The answer to this depends on the condition of the kidneys.

For healthy people with no kidney disease, no clear adverse effects have been confirmed. An analysis of 28 studies (involving a total of 1,358 healthy adults) found no difference in changes in kidney function even when protein intake was high [6]. Although the dietary reference standards state that the upper limit (tolerable upper intake level) should be set with the effects on the kidneys in mind, no limit has been established because the evidence is insufficient [5].

For people who already have kidney disease (chronic kidney disease), the situation is different. Clinical guidelines recommend restricting protein intake according to the severity of the disease [5]. People with kidney disease should avoid increasing their protein intake based on their own judgment and should always consult a doctor or registered dietitian.

Furthermore, there are no clearly defined signs such as “these symptoms appear when you consume too much protein.” Because excessive intake is difficult to notice, it is important to know the recommended amounts.

Protein produced in the body and dietary protein are two different things

In aging research, you may hear that “reducing protein makes you younger.” It is important not to confuse this with dietary protein.

A research team at Yokohama City University has studied cellular aging and rejuvenation for approximately 40 years. As part of this work, they reported that slightly suppressing the amount of protein produced in cultured cells made them less prone to aging (2016) [7]. This refers to protein that cells produce within themselves.

In contrast, this article discusses the amount of protein obtained from food. Even if dietary protein is reduced, the amount of protein produced in cells does not necessarily decrease in the same way. The company website’s research column, “Is Rejuvenation Possible?,” provides more information on cellular research.

What to keep in mind when reading protein research

Information about protein is frequently discussed in the news and on social media. When reviewing research results, it is recommended to check the following points.

• Observational study or trial: Studies that compare diet and subsequent disease (observational studies) can show that there is a “relationship,” but they cannot conclude that “protein was the cause.” People who consume more protein may also differ in other dietary and lifestyle habits.
• How the diet was assessed: In the American study, dietary intake was assessed through a one-day report. Also, the low-protein group was small, consisting of only 437 people. The size of the figures should be interpreted with a certain degree of flexibility.
• Animals or humans: Results from mice are only at the “possibility” stage until they can be confirmed in humans.
• Age and physical condition: Results may differ depending on age even within the same study. It is important to consider whether the findings apply to your own age and medical conditions.

Frequently Asked Questions

Q. Is it safer to consume a higher amount of protein?

A. Research does not show that “more is better.” There is an observational study showing that people who continued to eat a diet high in protein during middle age had higher rates of death from cancer and other causes. For now, it is best to use the range set by the national standards (around 13–20% of energy intake) as a guide for your daily diet.

Q. Should I reduce my protein intake as I get older?

A. No. As people age, inadequate intake is thought to be more problematic than excessive intake. In the American study, people aged 66 and older who consumed more protein also had a lower risk of death. The dietary reference standards also raise the lower limit to 15% for those aged 65 and older. Please pay particular attention to avoiding inadequate intake when your appetite decreases.

Q. Is animal-based or plant-based protein better?

A. Some studies have shown more favorable results for plant-based protein. A study that followed approximately 70,000 Japanese people also found that those who consumed more plant-based protein tended to have a lower risk of overall death [8]. However, this was also an observational study. The basic principle is to avoid relying on either source exclusively and to obtain protein from a variety of foods, including beans, fish, eggs, meat, and dairy products.

Q. How can I determine whether my protein intake is too high or too low?

A. The amount you need varies depending on your body type, activity level, age, and medical conditions. We recommend consulting a doctor or registered dietitian before making major changes to your diet. People with medical conditions such as kidney disease or diabetes should not change the amount on their own.

Summary

Most protein research consists of observational studies and animal experiments, and much is still unknown. Do not make major changes to your diet on your own, and consult a doctor or registered dietitian if you have any concerns.

Related Pages

• Company website research column, “Is Rejuvenation Possible?”

Citations and References

1. Levine ME, et al. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metabolism. 2014;19(3):407-417.
2. Solon-Biet SM, et al. The ratio of macronutrients, not caloric intake, dictates cardiometabolic health, aging, and longevity in ad libitum-fed mice. Cell Metabolism. 2014;19(3):418-430.
3. Zhang X, et al. High-protein diets increase cardiovascular risk by activating macrophage mTOR to suppress mitophagy. Nature Metabolism. 2020;2(1):110-125.
4. Houston DK, et al. Dietary protein intake is associated with lean mass change in older, community-dwelling adults: the Health, Aging, and Body Composition (Health ABC) Study. American Journal of Clinical Nutrition. 2008;87(1):150-155.
5. Report of the Study Committee on the Dietary Reference Intakes for Japanese (2025 Edition) (and “Key Points for Formulation,” February 2025), Ministry of Health, Labour and Welfare
6. Devries MC, et al. Changes in kidney function do not differ between healthy adults consuming higher- compared with lower- or normal-protein diets: a systematic review and meta-analysis. Journal of Nutrition. 2018;148(11):1760-1775.
7. Takauji Y, et al. Restriction of protein synthesis abolishes senescence features at cellular and organismal levels. Scientific Reports. 2016.
8. Budhathoki S, et al. Association of animal and plant protein intake with all-cause and cause-specific mortality in a Japanese cohort. JAMA Internal Medicine. 2019;179(11):1509-1518.