Study: High-protein diet and longevity

reference

Levine ME, Suarez JA, Brandhorst S, et al. Low protein intake is associated with significant reductions in IGF-1, cancer, and all-cause mortality in the 65 and younger population, but not in the elderly population.Cell metabolism. 2014;19(3):407-417.

design

Dietary protein consumption was examined in a US population cohort and looked for associations with all-cause and disease-specific mortality.

Participant

The studied cohort consisted of 6,381 adults aged 50 years and older from NHANES III, a nationally representative cross-sectional study. The median age was 65 years and was representative of the U.S. population in terms of ethnicity, education, and health characteristics.

Diet details

The subjects consumed an average of 1,823 calories per day, the majority of which came from carbohydrates (51%), followed by fat (33%) and protein (16%), with the majority of these (11%) coming from animal protein. The percentage of calorie intake from protein was used to categorize subjects into a high protein group (20% or more of calories from protein), a moderate protein group (10–19% of calories from protein), and a low protein group (less than 10% of calories from protein).

Target parameters

Mortality was tracked through the National Death Index until 2006, which indicates the time and cause of death. The 18-year follow-up period included a total of 83,308 person-years with an overall mortality of 40%; 10% were due to cancer, 19% to cardiovascular disease and 1% to diabetes.

Key findings

Study cohort members aged 50-65 years who reported high protein intake experienced a 75% increase in all-cause mortality and a 4-fold increased risk of cancer death over the following 18 years. These associations were either abolished or attenuated when the proteins were of plant origin. Conversely, high protein intake was associated with lower cancer incidence and all-cause mortality among respondents over 65 years of age. Those who ate a high-protein diet saw a five-fold increase in diabetes mortality across all age groups. These results suggest that low protein intake in middle age, followed by moderate to high protein consumption in older adults, may optimize health and longevity.

Effects on practice

This data suggests that people should change their eating habits in two important ways. First, patients under 65 years of age should be discouraged from consuming high-protein diets, especially diets high in animal protein. They should be encouraged to switch to plant-based protein. Second, patients over 65 should be encouraged to consume more protein as this will reduce overall and cancer mortality unless they are at high risk of diabetes.

What was striking was the increased risk of diabetes observed in the middle-aged population on high-protein diets: subjects without diabetes at baseline had a 73-fold increase, while those in the moderate protein intake group had a 23-fold increased risk of diabetes mortality. These increased hazard rates may be somewhat inaccurate due to the small sample size; There were only 21 diabetes deaths in people who did not have diabetes at baseline, and only one was in the low protein group.

Insulin-like growth factor 1 (IGF-1) was significantly lower in those 50 to 65 years old with low protein intake, while in those over 65 years old, the difference between the effects of high- and low-protein diets on IGF-1 was insignificant.

The differences in mortality reported in this study are not small. The researchers found that eating a diet rich in animal proteins in middle age puts you four times more likely to die from cancer than someone who eats a diet low in protein; This is an increased risk, comparable to smoking.

The study was actually more complex than presented in the summary above. It also included separate cell studies using yeast and animal studies using mice to examine the same questions. The influence of a high-protein diet on cancer progression was confirmed in mice implanted with melanoma cells. The tumors in the mice on a low-protein diet grew significantly more slowly and remained significantly smaller over the course of the experiment.

To test the hypothesis that older subjects on a low-protein diet become malnourished because they have difficulty absorbing amino acids, an experiment was conducted in which both young and old mice were fed either high- or low-protein diets. Old mice fed a high-protein diet for 30 days gained weight. Old mice, but not young mice, fed a low-protein diet lost 10% of their weight on day 15, supporting the conclusion that the effects of high- or low-protein diets may vary with age.

Mice have also been used to test the hypothesis that the growth hormone receptor and insulin-like growth factor-1 together promote cancer progression. Melanoma cells were implanted into growth hormone receptor (GHR)- and IGF-1-deficient mice along with normal controls. Tumor growth was much slower in the mice that had no GHR or lacked IGF-1.

Protein intake was also tested in mice that had been implanted with breast cancer. Differences could already be seen on the 18th day after implantation. The tumor incidence was 100% in the mice on the high-protein diet and only 70% in the mice on the low-protein diet. At the end of the experiment on day 53, the tumors in the mice on the low protein diet were 45% smaller.

Yeast was used to test the hypothesis that began to form after reviewing the human data suggesting that amino acid levels are linked to lifespan. Yeast was grown in media with different amino acid concentrations. By the fifth day of the experiment, the yeast exposed to high amino acids had a three to four times higher mutation rate. By day eight, yeast grown in high concentrations of amino acids had seen a tenfold reduction in the number of surviving cells.

The strong association between protein consumption, IGF-1, disease, and mortality observed in this study has not been observed in some previous reports; The age effect may not have been taken into account. For example, Saydah (2007) reported no increase in all-cause, cardiac, or cancer mortality when comparing the lower quartiles to the highest quartiles of protein consumption in the NHANES III data.¹

That the amount of animal protein accounts for a significant proportion of the association between total protein intake and all-cause and cancer mortality is consistent with other recent reports of the association between red meat consumption and deaths from all causes and cancer. Fung et al. reported in 2010 that a low-carbohydrate diet is associated with increased all-cause mortality.²

In 2009, Sinha et al. Data from the National Institutes of Health Diet and Health Study cohort of half a million people ages 50 to 71 reported that red and processed meat consumption was associated with increased all-cause mortality, cancer mortality, and cardiovascular disease mortality.³

Pan et al came to the same conclusion in 2012 after analyzing data from 37,698 men in the Health Professionals Follow-up Study and 83,644 women in the Nurses' Health Study. They reported that red meat consumption was associated with an increased risk of all-cause, cardiovascular, and cancer mortality. After documenting 23,926 deaths during 2.96 million person-years of follow-up, Pan et al. calculated that for each serving of unprocessed red meat consumed daily, the overall mortality risk increased by 13%. For processed red meat, one serving per day increased the overall risk by 20%. These researchers estimated that replacing 1 serving of red meat per day with other foods (including fish, poultry, nuts, legumes, low-fat dairy products, and whole grains) was associated with a 7 to 19% lower mortality risk.⁴

The idea that diets high in red meat are linked to mortality is not new.

Although these new diet suggestions are simple, we won't be surprised to see resistance from advocates of various popular diet plans. A number of common dietary strategies, including the Atkins diet and the Paleolithic diet, among others, can increase a follower's protein consumption to an extent that, if the conclusions of this study are correct, may negatively impact a person's health and increase the risk of diabetes. Cancer and early mortality.

Anyone advocating a high-meat diet for people under 65 should be ethically obligated to either find a flaw in this paper or find an overarching justification for such a diet that outweighs the impact of high protein on long-term survival. This idea that protein consumption should vary with age is a new concept not yet known to the public and will be difficult to explain. It might be a good idea to print out a copy and read the entire article yourself before attempting to speak to your patients.