What About Anti-Aging Diets?
Dr. Stephen Newdell
Diets that purport to slow the aging process are becoming increasingly popular. But are they worth the effort and discomfort?
The Proponents of these diets cite evidence that nutrient-restricting diets can increase healthy lifespan — at least in laboratory organisms such as yeast, worms, flies, and rodents.
In 1917, the journal Science published the first study to show that restricting the calorie intake of rats can delay the animals’ development and dramatically increase their lifespan.
More than 100 years on, the same journal published a roundup of the best research to date into the efficacy and safety of diets that claim to slow the aging process.
Scientists at the University of Washington in Seattle and Pennington Biomedical Research Center in Baton Rouge, CA, conducted the review of popular anti-aging diets.
These include not just caloric restriction but also diets that strictly limit a person’s intake of carbohydrates, proteins, or particular amino acids.
The scientists also reviewed the evidence for the efficacy of various fasting regimes.
Remarkably, most of these diets appear to exert favorable effects on health and aging through their influence on a single metabolic pathway that yeast, worms, rodents, and humans have in common.
In theory, existing drugs that target this pathway could reproduce the diets’ beneficial effects without the need to go hungry or give up particular types of food.
The authors caution that they may not work equally well for everyone.
For some people with a particular genetic makeup or under certain environmental conditions, the diets may actually be detrimental to health.
The reviewers emphasize that there are no clinically proven anti-aging diets and conclude that more research is needed before doctors can recommend such diets for otherwise healthy people.
This begins to sound like the ancient Japanese habit called Hari Hachi Bu, which is defined as eating until you feel 80% full and then stop eating and get up and away from the table. They did not use modern science. They used their feeling and their eyes and they’re still getting great results.
When researchers restrict the calorie intake of mice and rats — while providing all the essential nutrients they need — the animals are healthier and their average lifespan increases compared with animals fed an ordinary lab diet.
In addition, these rodents have a reduced incidence of age-related diseases, including cancer, neurodegenerative disorders, cardiovascular disease, and type 2 diabetes.
There is a clear inverse relationship between calorie intake and lifespan in the animals, up to about 50% calorie restriction. Animals that begin these diets while still young appear to reap the most benefits.
Whereas the results of research into calorie restriction in lab animals are clear-cut do they apply to humans. This is not so obvious.
Researchers typically house mice and rats in ideal, pathogen-free conditions and keep a close eye on their health.
By contrast, there are enormous variations in human environments and lifestyles which are likely to have a large impact on the health effects of potential life-extending diets.
Genetic variation between individuals is also likely to play a role in the diets’ outcomes.
Life length is determined by many things including emotional stress and physical work loads. Therefore, it is reasonable to assume that we will never get a complete scientific survey and picture of what a calorie restricted diet can do.
However, we see that people like the Chinese and Japanese, who live mostly on vegetables, are very long lived.
In addition, as much smaller creatures, mice have very different metabolic demands to ours. They have to burn around half of the calories they consume just to maintain their core body temperature, say the authors.
Another problem with translating the promising results in animal studies into humans is that our lives can span decades, whereas theirs only last a few years. Comparable studies in humans would be nearly impossible. How could we get a huge cross section of the world’s population and compare and for how long would such an experiment run? How many people would adhere to the diet? It seems like a project that cannot be done.
Risks and benefits
Extreme calorie restriction — which animal research suggests is likely to yield the greatest life extension — also comes at a cost.
We know from the relatively small number of people who manage to conform to such rigorous diets that potential side effects include:
- poor cold tolerance
- loss of libido and sexual function
- psychological problems
- chronic fatigue
- poor sleep
- muscle weakness
- increased susceptibility to infection, and,
- impaired wound healing
Severe calorie restriction can impair both immune function and wound healing, which could offset any potential lifespan-extending benefits under adverse environmental conditions in which the immune system is challenged, for example, a global viral pandemic, or in the absence of quality healthcare.
There is a question that hovers in the background. How long do you want to live and WHY? Do you really want to live to be an infirm 90-year-old dependent upon others?
We can observe small populations:
For example, the inhabitants of the small Japanese island of Okinawa traditionally consume 20% fewer calories than people who live on the mainland.
In the past, residents of Okinawa have enjoyed the longest life expectancy and the highest number of centenarians per head of population anywhere in the world.
Research suggests that they also experience exceptionally low rates of age-related illnesses, including cancer, cardiovascular disease, and diabetes.
However, as with all observational studies, the research cannot tell us whether calorie restriction is responsible for these health benefits or only partly responsible. It could be it is partly responsible and that their life span is extended because of other cultural, life style, and genetic factors.
While no clinical trial has tested whether there is an increase in overall lifespan with calorie restriction, a series of shorter trials lasting from a few months to 2 years have found clinical benefits that are likely to extend a healthy lifespan.
The studies have found that a 25% reduction in calorie intake is associated not only with decreased weight but also enhanced insulin sensitivity and glucose tolerance and improvements in risk factors for cardiometabolic disease.
Diets that strictly limit intake of carbohydrates but allow unrestricted consumption of healthy fats force the body to use molecules called ketones — a byproduct of fat metabolism in the liver — as fuel.
This kind of diet, known as a ketogenic diet, may reduce the frequency of seizures in people with epilepsy and promote weight loss in overweight and obesity.
In 2017, two studies reported that a low carbohydrate, low protein ketogenic diet increased the average lifespan of mice and improved the animals’ health in old age.
One of the studies found that the diet reduced mortality in midlife and improved memory in aging mice. The other study found that it increased longevity and a healthy lifespan.
The review authors note that the long-term effects of such diets in humans remain to be determined. But they go on to say that the animal findings are “highly suggestive” that ketones could have anti-aging properties.
There are many variations of fasting diets, but they fall into three broad categories:
Intermittent fasting typically involves consuming few or no calories for 1–4 days each week.
Fasting-mimicking diets induce the same metabolic changes by following a low calorie, low protein diet for around 5 days each month.
Time-restricted fasting restricts eating to a certain number of hours each day.
The authors of the review say most preclinical animal studies of these diets are effectively investigating different forms of calorie restriction.
This is because the animals in the experimental group usually end up consuming fewer calories than animals in the control group.
Thus, it is difficult to distinguish the potential benefits of fasting from the well-established benefits of calorie restriction.
But the reviewers do point to a study that compared mice allowed to eat only on alternate days with mice that consumed the same overall calories but without fasting.
This study found improvements in metabolism and reduced inflammation in the intermittent fasting group.
However, an equivalent study in people found that individuals who fasted every other day saw fewer benefits for their health than individuals who simply ate a calorie-restricted diet with the same overall energy intake.
The results for time-restricted fasting from animal and human studies are similarly conflicting.
The reviewers cite studies in rodents that found time-restricted fasting improved various measures of metabolic health and protected against an obesity-causing diet.
Research in humans has yielded mixed results for time-restricted fasting. Some studies have shown only mild improvements in health, whereas others have suggested detrimental effects on glucose metabolism.
Protein and amino acid restriction
The review authors note that numerous studies have found that restricting protein intake increases the lifespan of rodents and reduces age-related disease.
They report that while protein restriction in itself increases lifespan, the benefits are considerably weaker than those from calorie restriction.
In addition, say the authors, there is evidence that restricting dietary intake of particular essential amino acids, which the body is unable to synthesize for itself, can extend lifespan.
Animal studies suggest that restricting tryptophan, methionine, leucine, valine, and isoleucine is beneficial for increasing a healthy lifespan.
A Universal Aging Switch
Intriguingly, nutrient-restricting diets appear to increase longevity and reduce age-related disease through their effect on a small number of metabolic pathways.
Specifically, the diets tend to reduce levels of growth hormone, insulin-like growth factor, and a signaling molecule called mechanistic target of rapamycin (mTOR).
Research shows that these molecules are key hubs in a molecular mechanism that senses the availability of nutrients in the animals’ environment.
The job of this mechanism is to promote cellular maintenance and repair when nutrients are scarce but redeploy the organism’s resources towards reproduction when nutrients are plentiful.
According to the disposable soma theory, this mechanism reflects the trade-off that all organisms must make between staying alive and reproducing.
Future research should focus both on gaining a better understanding of the cellular and molecular mediators of anti-aging diets under highly controlled laboratory conditions as well as the impact of genetic and environmental variation on health outcomes associated with these diets.
For me, your author, there are always the questions about quality of life and extending the dying process. There’s a certain egocentric desire for dignity involved here. I would prefer to step off the stage of life in relatively comfortable condition, rather then to be painful, and a burden to others.
My life philosophy and theology is such that I do not fear dying. Those who are terrified of death will spend every penny they can lay hands on to live a little longer, but doing so brings no benefit. Such people needed earlier in life to seek after true wisdom instead of always seeking only after the comforts money can buy.
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