Do you live longer by eating less protein, or more?
The ideal protein level differs by life stage: in middle age less appears to be better, while after age 65 adequate protein is actually protective. What is clear: choose plant-based protein sources as much as possible and limit processed red meat.
The answer depends strongly on your age. People between 50 and 65 years old with a high protein intake had a 75% greater chance of early death in long-running research, and even four times the risk of dying from cancer, compared with peers who ate little protein. With diabetes the difference was even larger: fivefold mortality among high-protein users, regardless of age. But in people over 65 this picture reverses: higher protein intake turned out to go hand in hand with lower cancer and overall mortality. Animal research also showed that a low-protein diet was harmful to very old animals. In later stages of life the body simply needs more protein to prevent muscle loss and frailty.
What you eat matters at least as much as how much protein you take in. Eating more plant protein instead of animal protein, even replacing just 3% of your daily energy intake, was associated with 10% lower mortality and 11 to 12% fewer deaths from cardiovascular disease. People who replaced their processed meat products with plant-based protein sources saw as much as a 34% lower risk of death. Animal protein was specifically linked to higher cardiovascular mortality, although it did not produce higher overall mortality in all analyses. The combination of 'high animal protein plus high processed red meat' scores the worst.
In animal research, restricting protein, or specific building blocks such as methionine, leads to a longer lifespan and better metabolism. What this means for humans is still unclear: studies in humans exist, but are too limited for firm conclusions. What is certain is that too little protein is also a risk, especially for older adults: muscle loss and increasing frailty shorten life expectancy.
A recently published review disputes that high protein intake is inherently harmful and argues that the existing evidence is more nuanced. That review was, however, written by authors with ties to the meat and dairy industry, so weigh those dissenting voices with some caution.
This answer rests on several large studies in which tens of thousands of people were followed for many years, supplemented by reviews of animal and laboratory research and one systematic review. The age-dependent findings come from a study of more than 6,000 Americans over 18 years; the findings on plant versus animal protein come from research with a combined total of more than 500,000 participants. The association may reflect cause and effect, but that has not been established: people who eat a lot of plant protein also live differently in other respects. For the mechanisms via amino acid restriction, the evidence in humans is still thin; animal research is more convincing. A review with conflicting interests (ties to the meat and dairy industry) downplayed the harms of high-protein diets; the researchers themselves acknowledged a possible conflict of interest.
Does eating less help you live longer?
In laboratory animals the effect on lifespan is well established, but in healthy humans direct evidence is lacking. A moderate and sustainable eating pattern is wiser than extreme restriction; discuss major changes to your diet with a dietitian or doctor.
Do older adults need more protein than younger people?
Older adults likely need more protein than the standard guideline of 0.8 grams per kilogram suggests. As a healthy older adult, aim for 1.0 to 1.2 grams per kilogram per day, spread well across meals, and combine this with resistance training where possible.
Do you live longer on a vegetarian or plant-based diet?
A high-quality plant-based diet is associated with less premature death. However, eating strictly vegetarian or vegan has not been proven to be better than a varied diet that occasionally includes meat or fish.
Do you actually live longer if you structurally eat fewer calories?
In laboratory animals, eating less convincingly extends lifespan, but this has not yet been demonstrated for healthy people without excess weight. If you want to benefit from what has been shown, eating moderately less or following an interrupted eating pattern are the safest, most reasonably supported options.
Does it matter what kind of protein I eat, or does only the total amount count?
The type of protein matters: animal proteins and well-combined plant-based sources provide more building material for muscles than collagen or single soy products. The total amount counts too, but it is not the whole story.
How much protein can your body use in a single meal?
Your body can use more than 20-25 grams of protein per meal, especially when that protein is combined with carbohydrates and fats. Spread your intake across four meals of approximately 0.4 grams per kilogram of body weight for the best results.