Since the 1980s researchers have been conducting an experiment on rhesus monkeys by restricting their calories to see if a calorie restriction diet is beneficial in improving their health and ultimately slowing down aging, as it does in other species such as yeast, worms, flies, spiders, rats, mice, dogs, cows, among others the diet has been tested on.
Rhesus monkeys live around 27 years on average and are thought to be the most similar physiologically to humans — so it’s believed the results would be more translatable to humans. Pending the final results, I’ll go into what the current findings are, what they could mean, and whether or not the work is likely to be translatable to people practicing calorie restriction.
WISCONSIN RHESUS MONKEY CALORIE RESTRICTION DIET STUDY
The study began in 1989 where they introduced 30 male rhesus monkeys into the study and then a further 30 females and 16 males in 1994. The animals were randomized and then put into either the control group or the calorie restricted group.
Restriction of calories was done in phases: 10% reduction in calories based on individual primate ad lib caloric intake until they reached 30% restriction. Unlike the NIA study, this ad lib group were allowed to eat as much as they wanted.
The animals also received very good care and any conditions that developed during the study would be treated. The median survival for rhesus monkeys in captivity is about 26-27 years and a maximum lifespan of 40 years, with 10% reaching 35 years of age.
In 2009 we got a glimpse that calorie restriction in non-human primates seems to work and extends both healthspan and lifespan (1). Age-related mortality was slashed and control fed animals were 3-times more likely to die of age-associated diseases than the restricted monkeys; although at this point all-cause mortality between groups did not reach statistical significance.
The calorie-restricted animals were far healthier with a complete protection from diabetes; they also had less heart disease, fewer rates of cancer, less muscle loss with age, less brain atrophy, among other benefits. It has been reported that the calorie restriction monkeys also look a lot younger than their well-fed counterparts.
An update came in April 2014: The Calorie Restriction diet improved all-cause mortality and age-related mortality in primates (2). Age-related mortality includes deaths from cardiovascular disease, cancer, diabetes, arthritis etc.
All-cause mortality takes into account deaths from accidents, anesthesia, gastric bloat (accidentally caused by overcooked batches of food), and endometriosis (a non-fatal human disease).
Most of these may have been preventable deaths and were not caused by intrinsic aging and so a separate analysis for just age-related mortality was created to look at the effect of CR on deaths caused by aging and the diseases that are associated with it.
So far 63% (24/38) of the control animals have died from age-related causes compared to only 26% (10/38) of the calorie restricted group. This indicates that simply reducing calories can have a dramatic impact on the incidence of diseases with age.
For all-cause mortality, the control group had 1.8 times the risk of death from any cause compared to the CR group. Right now there are currently 12 CR monkeys a and only 6 control fed animals alive.
CR ‘anti-aging’ protocol: Although calorie restriction has improved average lifespan in the study at WNPRC, the effects of the diet on the monkeys metabolic, lipid and hormonal profile has been inconsistent with the changes that are observed in mice, rats, and humans.
Reasons for this could be that the reduction in calories was not sufficient to signal low energy availability to activate the pathways and responses that are involved in retarding aging in mammals.
However, even with the inconsistent results, the monkeys still benefited from a reduction in calories and stayed leaner, healthier, and younger for longer.
A sweet disaster: To understand why there might have been a longevity advantage in the CR group relative to the control group, even though the CR monkeys did not display the CR-phenotype, we have to take a look at the diet used in the study.
The monkeys in the Wisconsin study were fed a semi-purified diet which comprised of 65% carbohydrates with 28.5% coming from sucrose and the remainder from cornstarch vs the NIA study where the monkey’s chow comprised of 56% carbohydrates with only 3.9% coming from sucrose (3).
The high level of sucrose in the diet that the Wisconsin monkeys received could explain why there were more cases of diabetes in the controls of this study compared to the NIA controls; although interestingly there were two cases of diabetes in the young-onset monkeys in the NIA study whereas the WNPRC study reported a complete protection from diabetes in the CR animals.
Also, although blood glucose levels were lower in the WNPRC monkeys, they had very high levels of insulin in the controls and the CR diet brought it down to more appropriate levels.
In contrast with the NIA monkeys which had lower levels of insulin but slightly higher levels of glucose. Before the monkeys began the diet, they were monitored for a 3-6 month period to assess their caloric intake when they had free access to food so that the researchers could establish an individual baseline from which to reduce the calories from.
Given that high sugar diets stimulate appetite, the monkeys ate a generous amount of food during this period. Later in the study, the researchers found that the difference between the calorie restricted group and the control group dwindled to only 18% difference because the monkeys in the control group voluntarily reduced their calorie intake.
Monkeys normally do this with age, but this was fairly early in the study, so the researchers lowered the intake of the CR group further to establish a 30% difference once again. Although there were some exceptions, as not all monkeys had their intakes reduced further because of the appearance of the animal and was deemed too risky to the animal’s health. No further reductions in calorie intake in the CR group are being performed at this stage of the study, even if control animals still continue to decrease their intake in old age.
It was reported that 5 of the 38 monkeys of the Wisconsin control group developed full-blown diabetes vs only 5 out of 64 in the NIA control group (11% vs 8%). Diabetes incidence does have a strong correlation with increasing weight.
The NIA monkeys weighed less at all ages than the WNPRC monkeys. (2). In humans, the prevalence of diabetes (diagnosed) in the UK is as high as 5.8% in England, with the national average at 4.6% in 2013 (4). Earlier reports say at least 12% of deaths in the UK are a result of diabetes and its complications.
This means that the control group in this particular study represents more closely a typical western population in terms of diet and disease incidence.
Longevity phenotype: A lot of research has gone into the biology of aging in recent years. What is clear is that there is a specific phenotype that is common among long-lived individuals and families. Typically, they will have low levels of glucose and insulin. (diabetes cases being rare in those who reach 100).
Studies have shown a decreased functioning of the IGF-1 receptor and/or decreased levels of IGF-1 levels — which could be achieved by lowering protein intake to recommended daily levels of 10% of total calorie intake coming from protein (17) — leads to protection from diabetes, cancer and extends lifespan (5-8).
Lower levels of thyroid hormones have also been found in people with exceptional longevity: lower fT3, lower T4, and high-normal TSH can be exceptionally long-lived. (9,10). Higher HDL is protective; as well as lower levels of LDL cholesterol and triglycerides. (11).
Table 1 and 2 show the Wisconsin and NIA monkeys failed to display the changes that are typical with CR. In the Baltimore longitudinal study of Aging, men with lower insulin, lower body temperature, and high DHEA were found to be longer lived. Humans who voluntarily do CR (myself included) to display these changes with the exception of changes in T4 and TSH thyroid hormones which is mixed in humans.
Overall, humans seem to be responding more favorably to calorie restriction and more closely matches the phenotype displayed mice and rats that have a dramatically extended lifespan. I believe in order to understand the relevance to studies on aging, we must first understand if the study group actually responding properly to CR, as rodents and humans do.
A little extra weight is not good for you; dispelling the ‘myth’ that being overweight reduces the risk of mortality: Several reports have come out in the last few years suggesting that being overweight decreases mortality.
They typically either show a J-curve or a U-curve for BMI, which basically meant that being thin was associated with greater mortality and being obese is even worse; but being slightly overweight was actually good for you. (12).
They came to this conclusion by looking at a large number of people and excluding all obvious causes of being thin: smoking, alcohol abuse, and pre-existing diseases were controlled for to see what is the optimal BMI in humans. Unfortunately, these studies fail because of serious methodological flaws and the inability to control for leanness because of a healthy lifestyle, rather than poor diet and ill health.
Healthy individuals eating a diet that is rich in vegetables, fruits, nuts, seeds, and fish are likely to represent a very small fraction of lean individuals. Indeed, one study that was conducted by Cardiff University found that only 15 men out of 2,235 men ate more than 5 fruits and vegetables a day. Less than 1% followed all 5 healthy behaviors. Following a ‘healthy lifestyle’ is not common here in the UK (13).
This indicates that being thin in the general population is more likely to be a result of poor lifestyle choices and/or underlying diseases than to a healthy lifestyle — which in many studies has been correlated with lower rates of mortality. In fact, just recently it was reported that eating 7 more fruits and vegetables a day is associated with a 42% reduction in mortality. And the more fruits and vegetables consumed, the lower the BMI. (14).
If we agree that this study does not represent a true ‘anti-aging’ study because the CR group were not restricted enough to elicit many of the CR responses that drives its ‘anti-aging’ effect; and that the controls were also overfed, then this study represents what the general population could expect if they were to reduce their calories a little and maintained a healthy body weight.
Both Wisconsin and the NIA primate studies show that lowering body weight is very important to health and lifespan. And whether or not there is diminishing returns in the effect CR has on lifespan as body weight is progressively decreased, there should be no doubt that excess body weight is bad news when it comes to diseases of aging such as diabetes, cardiovascular disease, and cancer. These are some of the biggest killers in western countries today.
These studies show that changing dietary habits can have a dramatic impact on your disease risk and that you have more control than you might think. You are not destined to develop the same diseases as your family and friends if you act now to live a healthier lifestyle. As this study shows, you could potentially add years to your life. And you’ll see the effect on quality of diet plus staying lean is even greater still!
NIA RHESUS MONKEY CALORIE RESTRICTION STUDY
In this study, they had two groups on the diet to establish what effects CR has on health in young animals and old animals. The study conducted at NIA was more in-line with rodent experiments where the control group was restricted by 10% to avoid the effects of obesity, whilst the CR group are restricted by 30%.
Energy intakes were calculated from tables of energy intake requirements for the rhesus monkeys by age, weight, and gender. Both groups received a relatively healthy diet that was also supplemented with 40% extra vitamins and minerals to ensure that the calorie restriction group met the recommended daily intake for all nutrients. However, as the control group also received the same diet, this meant they were super-supplemented. The NIA-1-87 formulation.
The diet is also naturally based and contains many phytochemicals and other micronutrients that are beneficial to health and could in synergy with CR to improve health. During the course of the study, measurements were made to see what effects CR had on the monkey’s health.
Young-onset: In the CR’d male monkeys there was no effect on glucose levels compared with the controls. In the females, there was only a very slight reduction. Triglycerides tended to increase with age across all groups; interestingly, young-onset CR’d females experienced a significant increase in triglyceride levels compared to the control female group (15), which is bizarre, because, in humans, there are no differences by gender in the response to CR when it comes to the dramatic lowering of triglycerides.
The monkeys also failed to exhibit several other distinct changes that usually occur with CR: There was no reduction in testosterone or estrogen as we see in rodents and humans. And no increase in the stress hormone cortisol.
Serum triiodothyronine (T3) was reduced by 14% in the young and old CR’d female monkeys and very little effect in males. In humans practicing vigorous CR, there is a major reduction in T3; but this was not observed when overweight people who had lost weight to get within the healthy BMI range like those in the CALERIE study (more on that later).
Old-onset: In males, there was a significant decrease in cholesterol in the CR’d group. Glucose was also reduced significantly, while there was only a modest effect was seen in CR’d females. Triglycerides were significantly reduced in CR males and modestly reduced in CR females. (15).
Blood pressure was not affected in the monkeys; which is inconsistent with the data in humans, as we see a dramatic decrease in blood pressure from average values for their respective ages to levels that of a child: approx 100/60. (16) Indicating once again that humans respond better than monkeys to CR.
CR has a dramatic effect on cancer if started young: It’s worth noting that one significant effect has been found in the young-onset monkeys: so far none of the calorie-restricted monkeys have developed cancer (CR 0/40 vs 6/64 AL) Calorie restriction initiated early in life is powerful in protecting against cancer in rhesus monkeys and possibly humans.
This is one effect that is consistent with what we see in rodents. Unlike old-onset rhesus monkeys, the young-onset do see reductions in IGF-1 levels, which may partly explain this effect (although not entirely). In humans, practicing vigorous CR with protein restriction (10% of calories), both young and old see significant reductions in IGF-1. (17).
Longest lived rhesus monkeys on record: Although survival was the same for both groups in the old-onset group (35.4 years), this was significantly longer than previously reported median lifespan of just 27 years for a rhesus monkey in captivity. (15).
Not only that, of the 20 male monkeys in the old-onset group, 4 monkeys in the calorie-restricted group have lived beyond 40 years and only 1 control monkey. 40 years is considered the maximum lifespan for a rhesus monkey. Researchers analyzed data on the lifespan of 3264 rhesus monkeys, and only two 40-year old monkeys have ever been documented.
According to researchers, one year for a monkey is roughly equivalent to 3 human years. (1). So 35.4 years for a rhesus monkey would correspond to about 106 human years? Rhesus monkeys in this study in both old-onset groups gained 8-years of extra life; equivalent to 24 human years. As the study is still about 10 years away from being completed, I would expect that we could see a few more 40-year old monkeys in the young-onset group.
The NIA group had a fairly significant survival advantage over all groups in the WNPRC study. With a 10% restricted healthy diet, the NIA cohort broke longevity records.
Is it possible that the 10% reduction in calories with a very healthy diet that was rich in vitamins, minerals, phytochemicals, omega-3 fatty acids was additive in its effects with CR so that the 10% CR group effectively got the same benefit as the 30% restricted group?
As these monkeys have lived far beyond what is typical for a rhesus monkey, it’s clear that the quality of diet matters a lot; and being lean is very beneficial for health and longevity.
In studies on rodents, 10% CR can effectively extend lifespan as much as 30%; but this is not true of all strains. In most, the lifespan gained is in proportion to the degree of restriction and the length of time the animal has been restricted.
Translation of ‘monkey years’ to ‘humans years’ might not be exact; it’s just a rough estimate.
CALORIE RESTRICTION DIET IN HUMANS
At least 18 people practicing calorie restriction with optimal nutrition have been studied by Dr.Luigi Fontana at Washington University in St Louis. In a study published in 2004, medical records were collected of the participant’s previous health data which included things such as body weight, blood pressure, glucose, cholesterol etc to see what effect years of calorie restriction has had on health. Those doing calorie restriction were very lean with a BMI of 19.6 ± 1.9 vs 25. ± 3.2 kg/m2 for the western diet group. Average time on CR was 6 years ± 3 (range 3 to 15 years).
Just recently participants from the CR society had their muscle biopsied and analyzed to look at gene expression profiles compared to that of 30-year-old controls and age-matched controls (58 years), and also they compared the molecular changes in rats on 40% CR. They hypothesized that CR in humans would have induced a down-regulation of the Insulin/IGF-1/FOXO pathway which has been linked with longevity in animals and humans (20-22).
What they found was a very significant down-regulation of the Insulin/IGF-1/FOXO pathway at the transcriptional and post-transcriptional level. The key changes in skeletal muscle gene expression profile that are observed in long-lived rats are also observed in humans.
So not only are humans responding at a physiological level to CR as animals do, but the molecular adaptations seem to mirror that of mice and rats. They also looked at SIRT 1 and AMPK: these two energy-sensing pathways were significantly up-regulated in people on CR.
FOXO3A and FOXO-4 were significantly up-regulated: these are known to modify many ‘longevity genes’ in animals and increase activities such as DNA repair, antioxidant defenses, immunity, protein turn over, and cell death genes. (22). Autophagy, which helps remove dysfunctional cell components to recycle was also significantly up-regulated by CR.
Looking at (Figure 1b (23)), it looks as if people on CR had more similar gene expression profiles to the younger individuals in the study. The ‘gene expression’ of people on CR is more like that of a 30-year-old than the age-matched 58-year old control group. This is a very important finding to see if the same response to CR is conserved across species. The study found that major risk factors for cardiovascular disease were reduced significantly in people on CR.
The average Total cholesterol and LDL-C concentration for the CR group were in the lowest 10% for people in their age group (50 years). Also, even more dramatic, the levels of triglycerides in the CR group were lower than 95% of Americans who are in their 20s. And their HDL (good cholesterol) was higher than 85-90% of people in middle age.
Fasting insulin was 65% lower than the western diet group and glucose was also significantly lower too. People on CR have also been found to have lower body temperature, lower thyroid hormone T3 as well, but people who exercise vigorously and maintained a similar BMI did not see these reductions. (29,31)
Participants of the study also had extremely low blood pressure, equivalent to that of a 10-year old. They had almost non-detectable or very low levels of inflammation measured by c-reactive protein. The IMT carotid artery thickness was measured and found to be 40% less in the CR group compared with the controls: 0.5 ± 0.1 mm in the CR and 0.8 ± 0.1 mm for controls. None of those eating a CR diet had any evidence of atherosclerotic plaque.
To show the powerful effect that CR had on their health, the researchers were able to gather medical records from 12 of the individuals in the CR group and show that just like the western diet group, values for the CR group were average (50th percentile) before embarking on the diet.
Possibly even more impressive results showing that CR in humans might be slowing down the rate of aging of the heart. They looked at the diastolic function of the heart and its ability to relax and fill the left ventricle and found that people on CR had hearts that were similar to those who were 15-years younger (17).
And those on the diet also had the heart rate variability of a person 20 years younger. (18) It looks as if CR must have had a rejuvenating effect on heart function and wasn’t just merely slowing its decline in function and performance.
WIll calorie restriction work in humans?
Looking at the data we have thus far from mice, rats, rhesus monkeys, and humans, we are able to make comparisons to see the differences between each species in how they react at a molecular level and at the physiological level to CR; and also how they react to the various degrees of calorie restriction. It’s clear that people on a calorie restriction diet do display a more CR-like state than either the NIA or Wisconsin rhesus monkey studies.
Not only that, people in the CALERIE study who were overweight and merely reduced their body weight to a ‘healthy’ weight from a BMI of 27 to 24 with 25% CR, never exhibited several CR signatures, nor did they have as significant reductions or changes in total cholesterol, LDL-cholesterol, triglycerides, inflammation, thyroid hormone levels, testosterone, estrogen, IGF-1 and cortisol.(26-28).
All of these are strongly influenced in people studied at WUSTL who are from the CR Society and practice moderate-severe CR. (16-19, 23). Many of these signatures that were not observed in the CALERIE study were also either not observed in the CR primate studies, very inconsistent, or modest in their change or effect. (25-28). This indicates that the level of CR in the primate studies, as well as the CALERIE human study, were insufficient to elicit the key changes that are responsible for the age-retarding effect of CR.
Apart from the CR being insufficient to elicit these changes, another possibility could be that the declining difference between energy intakes of the NIA rhesus monkeys (20% less than ad lib for males and only 12% for females) could be the reason why little differences were seen. It was reported also that the calorie-restricted monkeys did not exhibit much sign of hunger during the study either; another argument pointing to the fact that the CR group needed to be restricted further.
Before embarking on this very long study, it may have been wise to restrict monkeys to various degrees to see if there is a ‘cut-off point’ to where CR does not improve their health further. If they display the CR-phenotype in a more consistent and powerful way, then establish this level of restriction for the CR group for a lifespan study, as long as the level of restriction was not inhumane and the animals did not display poor health from it.
We have a lot more control over our own diets, exercise, and supplements than animals who are subjected to these diets. The interactions between all of these are only just now being discovered. It’s only a matter of time before we’ll have reliable markers of aging which we can use to see if our diets are working. In response to the results we see with the diet, we are able to change accordingly to get into the most optimal and CR’d-like to have the best chance for living longer and healthier lives.
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