In yet a new twin study funded by the National Institute of Health’s NIA and USC Norris Cancer Center and published in the journal Cell Metabolism, (Exhibit A), it was shown that a high-protein diet during middle age was associated with higher mortality while in adults over 65, a low-protein diet was linked with worse outcomes. One of the key findings of these studies concludes that high animal protein intake can be as bad as cigarette smoking.
“We studied simple organisms, mice, and humans and provide convincing evidence that a high-protein diet—particularly if the proteins are derived from animals—is nearly as bad as smoking for your health,” says the University of Southern California’s Dr. Valter Longo, who is the senior author of one of the papers. (Source)
As the Science on Longevity has demonstrated for close to a century, caloric restriction increases longevity in mammals. However, it was not known via what mechanism of action, meaning, if the restriction works by lowering calorie intake or by reducing the intake of protein, meat or other nutrients. The team led by Dr. Valter Longo analyzed information on more than 6,800 U.S. adults, ages 50 and over, from the Third National Health and Nutrition Examination Survey (NHANES III), a periodic health and nutritional survey of the U.S. population. The researchers linked the survey data with National Death Index data, which provides the timing and causes of death. Therein, participants were categorized into 3 groups based on the percent of self-reported calorie intake that came from protein: high (20% or more), moderate (10-19%), or low (less than 10%). They were further split into 2 age categories: 50 to 65, and 66 and older. Adults in the 50 to 65 group who reported a high protein intake had a 75% increase in overall mortality and were 4 times more likely to die from cancer during the following 18 years than those in the low protein group. The moderate-protein diet was associated with a 3-fold increase in cancer mortality compared to the low-protein diet.
These associations (which were adjusted for numerous factors including smoking, waist circumference, and chronic conditions) weren’t altered when the percentage of calories from fat or carbohydrate were considered. However, the associations were only found when the proteins were derived from animal, rather than plant, sources.
Conversely, in participants ages 65 and older, those who consumed high amounts of protein had a 28% lower risk of dying from any cause and a 60% lower risk of dying from cancer. These associations weren’t influenced by whether the protein was derived from animal or plant sources.
On the other hand, a high-protein diet was also associated with a 5-fold increase in diabetes mortality across all ages. One limitation of the study, the researchers note, is that the participants’ protein intake was based on a single 24-hour dietary recall. The study also didn’t examine the effects of specific types of plant- or animal-derived proteins, such as beef or fish.
THE MODULATION OF THE IGF-1 PATHWAY
Mice fed a higher protein diet had increased progression of breast and melanoma tumors than those fed a lower protein diet. The low-protein diet, however, had detrimental effects in very old mice. The link between diet and longevity appeared to be moderated by a pathway involving insulin-like growth factor 1 (IGF-1).
“The research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality, through a process that involves regulating IGF-1 and possibly insulin levels,” says co-author Dr. Eileen Crimmins. “However, we also propose that at older ages, it may be important to avoid a low-protein diet to allow the maintenance of healthy weight and protection from frailty.” (Exhibit A)
ANALYSIS AND CONCLUSION
This conclusion is not surprising because other authors have corroborated similar results. However not all nutrition experts agree.
Prof Tom Sanders, Head of the Nutritional Sciences Research Division, King’s College London, wrote:
“The headline of the press release from the University of Southern California is running ahead of the evidence, and the comparison with smoking is really unwarranted in terms of the relative risks and the certainty of the adverse effects of smoking. The study shows a relationship with growth factor IGF-1 and cancer risk which is already known. However, the relationship between IGF-1 levels and protein intake is far more tenuous in humans. Cross-sectional data i.e. omnivores vs vegans suggest animal protein to be associated with increased IGF-1 levels but there is a lack of evidence from controlled feed studies to show that IGF-1 levels fall when animal protein intake is restricted. Much of the supporting work is based on studies in mice not humans. Dietary guidelines should not be based on animal experiments. “Although the follow-up on the NHANES survey* shows that those with the highest reported protein intake were at greater risk of all-cause mortality, it fails to adjust for other confounding factors such as socioeconomic status, smoking, and obesity. The sample size is also modest at 6381, compared with over 448,568 in the European Prospective Investigation into Cancer which only found a weak association (14% increase in risk of mortality with red meat consumption, which was more consistent for processed meat (11% increase in risk)). The European data suggest a much smaller effect than the 74% increased risk claimed in this paper….Also, the study does not control for the overall balance of the diet. People who eat large amounts of animal proteins often have other aspects of their diet which are imbalanced such as low intakes of fruit and vegetables. I think the next step would be to show that changing protein intake in the range of normal human intakes influences IGF-1 levels. IGF-1 levels may well be programmed in early development and dietary protein intake in adult life may well be less important in later life. This would be consistent with the observation that accelerated growth in childhood is associated with increased height and a high risk of cancer in later life.” (Source)
Professor Tim Key, a Cancer Research UK epidemiologist based at the University of Oxford, said:
“This study is too small to provide any robust conclusions. This area of research is important, but further research is needed to establish whether there is any link between eating a high protein diet and an increased risk of middle aged people dying from cancer.
“There is, however, strong evidence that the following things can help reduce your risk of cancer: giving up smoking, keeping a healthy weight, drinking less alcohol and staying physically active.” (Source)
Dr Gunter Kuhnle, a food nutrition scientist at the University of Reading, stated:
“While this study (Levine et al) raises some interesting perspectives on links between protein intake and mortality, it’s certainly not true that this is the first study to make such a link. It is also wrong, and potentially even dangerous, to compare the effects of smoking with the effect of meat and cheese in such a way….Sending out statements such as this can damage the effectiveness of important public health messages. They can help to prevent sound health advice from getting through to the general public. The smoker thinks: ‘why bother quitting smoking if my cheese and ham sandwich is just as bad for me?’…Other research, from long-running studies in Iowa and Sweden, already suggests that diets very high in animal protein increase mortality risk – particularly from those with diets very high in red or processed meat. Sabine Rohrmann has shown recently in a much larger European study that the increased risk of mortality from processed meat is about 20% (relative risk) for every 50g per day increase. This compares to studies into smoking, which suggests a doubling of mortality risk for smokers compared to non-smokers. The increased risk of cancer for smokers is higher still.” (Source)
Heather Ohly, Associate Research Fellow at the University of Exeter Medical School’s European Centre for Environment and Human Health, and Registered Nutritionist, indicated:
“While these new studies highlight important concerns about excessive dietary habits, it would be a shame if extreme headlines caused yet more confusion among the public about food and nutrition. Smoking has been proven to be entirely bad for us, whereas meat and cheese can be consumed in moderation as part of a healthy diet, contributing to recommended intakes of many important nutrients. However, excessive consumption of these foods will take people over the recommended intakes of saturated fats and protein, which may be harmful as indicated by these studies. In the UK, it is recommended that protein makes up 10-15% of our average daily energy intake. It is a good idea to consume a range of protein sources to obtain the full range of amino acids – the building blocks of protein – which all have different roles in the body. Plant sources of protein include nuts, seeds, beans and lentils. Nutritionists recommend including these foods in your diet as well as animal sources of protein such as meat, fish, cheese, milk and eggs. A key message from the study is “don’t get extreme in cutting out protein”. Just be sensible about where it comes from, choose high quality whole foods, and don’t over-consume any one food group”. (Source)
For Dr David Le Couteur, he is more hopeful and positive with this research.
“The advice we are always given is to eat a healthy balanced diet, but what does that mean? We have some idea, but in relation to nutritional composition we don’t know terribly well,” said co-author Dr. David Le Couteur, Professor of Medicine at the University of Sydney’s Charles Perkins Centre in Australia. “This research represents an important step in finding out.” (Source)
Professor Stimpson is equally more optimistic.
“We have shown explicitly why it is that calories aren’t all the same—we need to look at where the calories come from and how they interact,” said senior author Dr. Steve Simpson, Professor and Academic Director of the Charles Perkins Centre. “This research has enormous implications for how much food we eat, our body fat, our heart and metabolic health, and ultimately the duration of our lives.” (Source)
While all of these peer-reviewed assessment may have a point, the hard evidence from this NIA twin study, combined with other studies that we have shown elsewhere, including from Drs Esslstyn Campbell, Furhman, McDougall and Neal do confirm that high to moderate intake of meat can be comparable to tobacco smoking for cancer and other diseases. Meanwhile what this twin study have proven beyond any reasonable doubt is the following: 1). High to moderate protein intake is linked to increased cancer, diabetes, and overall mortality 2). High IGF-1 levels increased the relationship between mortality and high protein. 3). Higher protein consumption may be protective for older adults. 4). Plant-derived proteins are associated with lower mortality than animal-derived protein. But it will take a while for mainstream nutritionists, physicians and academicians to change opinions, given that their own intake of animal foods can be addictive to the brain making reasoning defective. Ch. J.
The first study suggests that consuming moderate to high levels of animal protein prompts a major increase in cancer risk and mortality in middle-aged adults, while elderly individuals have the opposite result. Meanwhile, the second team of researchers found that a high-protein, low-carbohydrate diet led to a shorter lifespan in mice. Both studies find that not all calories are created equal, diet composition and animal protein intake are key players in overall health and longevity.
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. Levine ME, Suarez JA, Brandhorst S, Balasubramanian P, Cheng CW, Madia F, Fontana L, Mirisola MG, Guevara-Aguirre J, Wan J, Passarino G, Kennedy BK, Wei M, Cohen P, Crimmins EM, Longo VD. Cell Metab. 2014 Mar 4;19(3):407-17. doi: 10.1016/j.cmet.2014.02.006. PMID: 24606898.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3988204/
Mice and humans with growth hormone receptor/IGF-1 deficiencies display major reductions in age-related diseases. Because protein restriction reduces GHR-IGF-1 activity, we examined links between protein intake and mortality. Respondents aged 50-65 reporting high protein intake had a 75% increase in overall mortality and a 4-fold increase in cancer death risk during the following 18 years. These associations were either abolished or attenuated if the proteins were plant derived. Conversely, high protein intake was associated with reduced cancer and overall mortality in respondents over 65, but a 5-fold increase in diabetes mortality across all ages. Mouse studies confirmed the effect of high protein intake and GHR-IGF-1 signaling on the incidence and progression of breast and melanoma tumors, but also the detrimental effects of a low protein diet in the very old. These results suggest that low protein intake during middle age followed by moderate to high protein consumption in old adults may optimize healthspan and longevity.Copyright © 2014 Elsevier Inc.
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