Is a High Protein Diet Unhealthy?

  • 2 Minutes Read
  • Mar 25, 2014

High protein dieters take notice: recent studies on mice and humans suggest high protein intake, as a percent of calories, significantly increases cancer mortality, and increases overall mortality.

Is a High Protein Diet Unhealthy?

Recent headlines would certainly give Paleo diet devotees cause for concern: high protein diets are as risky as smoking. The study in question found that middle aged people who eat more than 20% of calories as protein are 4 times as likely to die of cancer as people who eat less protein. But that wasn't all the study found. Let's take a closer look.

The study followed more than 6000 people for 18 years, surveying their diets and health. And in fact, people in the age range 50-65 who ate high protein diets, especially from animal protein foods, had major increases in risk for cancer deaths, as well as higher overall mortality. But there's a twist: the subjects who were older than 65 actually had lower mortality risk if they ate a high protein diet.

Why the difference? One possible explanation is that, as people age, the ability to digest and utilize protein decreases. So eating more protein in old age is necessary to be sure enough protein is metabolized. The official daily protein intake recommendations for older people aren't different from those for younger adults, but some experts on aging believe those recommendations should be increased. This study may support their belief.

There's another way to look at that result: older people may eat fewer calories, if they become less active with age. But if they maintain their same protein intake, the percent of protein would seem to go up. Let's say you typically eat 1800 calories/day in your 50's, and 15% protein ,which is about 67 grams per day. Not a big protein intake. But in your late 60's, you become less active, your appetite decreases, and your food intake falls to 1400 calories/day. Yet you still eat the same amount of protein - 67 grams/day. Your protein percentage is now almost 20%, a high protein intake according to this study, a healthy range for an older adult.

To further investigate the protein effect, researchers also looked at mice, fed diets with different protein concentrations. Result: The mice eating the highest protein diets were thinner, but their lives were 30% shorter. One possible reason: in the mice, high protein intake boosted certain gene activity that promoted tumor growth.

So is a high protein diet unhealthy? If excess protein increases gene activity that promotes cancer growth, then high protein by itself could be a bad idea. But the adverse effect could also be due to what high protein diets don't include. If your plate is loaded with meat, then there's not much room left for vegetables, grains, nuts, fruits and legumes. Meaning, you're lacking all the fiber, minerals, vitamins, antioxidants and healthy fats from those types of foods.

It's a dilemma for dieters. Excess weight and chronic diseases are unhealthy. High protein diets can help with weight loss. Plus, if you're restricting calories, your percentage of protein may look high, even though your grams of protein are moderate. On a 1200 calorie diet, 20% of calories is only 60 grams of protein, which is an adequate - not excessive -- protein intake for many adults. Eating a lower percent of protein on 1200 calories would mean eating inadequate protein.

The Takeaway Message:
If you use a higher protein diet for weight loss, you should transition to a moderate (but adequate) protein diet after you reach your target weight. That just makes sense anyway: larger portions of plant-based foods like vegetables, whole grains, fruit, and smaller portions of meats, dairy, eggs and fish. In other words, a Mediterranean-style eating plan, which is linked to better health in general.

Meal Planning & Diets->High Protein Nutrients->Protein
Donna P Feldman MS RDN is author of "Feed Your Vegetarian Teen", writes about food and nutrition at Radio Nutrition and is co-host of the Walk Talk Nutrition podcast series.
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