March 5, 2014
News Review From Harvard Medical School -- Age May Alter Cancer-Death Risk from Meat
Eating more meat in middle age may increase people's risk of death, particularly from cancer, a new study finds. But older adults who ate more protein lived longer than those who ate less. The study was based on diet surveys from more than 6,800 adults. Researchers kept track of deaths during the next 18 years. People were divided into 2 groups: middle aged (50-65) or older (over 65). Diets with at least 20% of calories from protein were classified as high-protein. Middle-aged people with high-protein diets were 75% more likely to die during the study period than those with low-protein diets (less than 10% of calories). They were 4 times as likely to die of cancer. Cancer-death risk was 3 times as high in the moderate-protein group (10% to 19% of calories). Most protein came from meat and dairy products. But the increased death risk was lower or disappeared for people who ate mainly plant protein such as beans. Older adults with high-protein diets were 60% less likely to die of cancer than the low-protein group. They were 28% less likely to die of any cause. The journal Cell Metabolism published the study. HealthDay News wrote about it March 4.
By Howard LeWine, M.D.
Harvard Medical School
What Is the Doctor's Reaction?
Some animals can live longer if they eat a restricted number of calories. The extension of life span can be dramatic. This may also be true for humans, but it's far from proven.
If calorie restriction does improve overall health and increase life span, it's likely that what's in the diet will have a big influence. For example, sugary foods and drinks raise your risk of developing diabetes, high blood pressure and heart disease. That is true even if you have reduced your total daily calories.
A new study focuses on protein in the diet. Researchers explored how the amount and types of proteins that people eat influenced the risk of certain health problems and early death.
They knew that people with low activity of one type of growth hormone are less likely to develop cancer and diabetes. And they live longer.
In mouse studies, protein restriction can decrease the activity of this hormone. But a high-protein diet in mice ramps up the hormone activity. This leads to a high risk of cancer and diabetes and a shorter life span.
In the current study, the researchers used data from a study on 6,381 men and women ages 50 and older. The study did extensive surveys of people's diets. Then researchers kept track of them for the next 18 years. During that time, 40% of them died:
- 19% from heart disease, stroke or other blood vessel disease
- 10% from cancer
- 1% from diabetes
- 10% from other causes
The results were extremely interesting. Adults ages 50 to 65 who reported a high-protein diet had a 74% increased risk of dying during the 18 years of follow-up. They were 4 times as likely to die from cancer as those who ate less protein.
And the sources of protein mattered -- a lot. The people in this age group generally got most of their protein from animal sources. But for those who ate mostly plant proteins, even in higher amounts, there was minimal difference in health outcomes and death rates compared with the low-protein eaters.
However, the opposite was true for older adults, the ones 66 and over. Those who ate high-protein diets, including both animal and plant sources, had a lower cancer risk than those who ate less protein. Their risk of death during the study period was also lower.
What Changes Can I Make Now?
If you are between the ages of 20 and 65, you likely need less protein than you think. A good goal is 0.7 to 0.8 grams of dietary protein per kilogram of body weight daily. For example, a 150-pound person weighs 70 kilograms. Multiply that by 0.8 and you get 56 grams of protein. You would get that much protein from 8 ounces of fish or a similar portion of beans.
Later in life, after age 65, your daily protein goal should be higher. Aim for 1.0 to 1.2 grams of protein per kilogram of body weight, especially if you are thin. Those who are heavier can aim for 0.8 to 1.0 grams of protein daily for each kilogram of weight.
Try to get most, if not all, of your protein from plants, fish and eggs. You can also get some protein from dairy sources.
What Can I Expect Looking to the Future?
In recent years, we have seen quite dramatic changes in what is considered a healthy diet. Not that long ago, a high-carb, low-fat diet was promoted as the healthiest.
Now we have moved completely away from that advice. The right fats, such as olive oil, are actually good for you. Sugary carbs should be avoided. And now we learn that restriction of protein, especially animal protein, may help us live longer.
You can expect to see more studies that help guide our dietary choices to promote better health.