Calorie restriction

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Effects of CR on different organisms
Primates

Researchers at New York's Mount Sinai School of Medicine reported in 2006 that compared to monkeys fed a normal diet, squirrel monkeys on a life-long calorie-restrictive diet were less likely to develop Alzheimer's-like changes in their brains.[12] Since squirrel monkeys are relatively long-lived, definitive conclusions regarding whether or not they are aging slower are not yet available. A study on rhesus macaques was started in 1989 at the University of Wisconsin-Madison. Preliminary results show lower fasting insulin and glucose levels as well as higher insulin sensitivity and LDL profiles associated with lower risk of atherogenesis in dietary restricted animals.[13]

Mice

Studies in female mice have shown that estrogen receptor-alpha declines in the pre-optic hypothalamus as they age. The female mice that were given a calorically restricted diet during the majority of their lives maintained higher levels of ERα in the pre-optic hypothalamus than their non-calorically restricted counterparts.[14] Studies in female mice have shown that both Supraoptic nucleus (SON) and Paraventricular nucleus (PVN) lose about one-third of IGF-1R immunoreactive cells with normal aging. Old caloricly restricted (CR) mice lost higher numbers of IGF-1R non-immunoreactive cells while maintaining similar counts of IGF-1R immunoreactive cells in comparison to Old-Al mice. Consequently, Old-CR mice show a higher percentage of IGF-1R immunoreactive cells reflecting increased hypothalamic sensitivity to IGF-1 in comparison to normally aging mice.[15][16]

Rats

Seventy years ago, McCay CM, et al., discovered that reducing the amount of calories fed to rats nearly doubled their lifespan. For the last seventy years, scientists have proposed hypotheses as to why. Some explanations included reduced cellular divisions, lower metabolism rates, and reduced production of free radicals generated by metabolism.

Yeast and invertebrates

Recently, Harvard professor David A. Sinclair has conducted research that provides a new explanation for the lifespan extension caused by calorie restriction. It involves the activation of a gene called Sirt1. When Sirt1 gene activity is increased by genetic manipulation, caloric restriction does not increase it any further. Knocking out the Sirt1 gene also eliminates any beneficial effect from caloric restriction. Resveratrol has been demonstrated to increase the activity of the Sirt1 gene the same way caloric restriction does. When resveratrol increased the subject's lifespan, caloric restriction failed to increase it any further. Presently, Sirt1 gene activity has not been increased in rats by genetic manipulation.

Drosophila

Research in 2003 by Mair et al. showed that calorie restriction extends the life of fruit flies of any age with instantaneous effects on death rates.[17]

Caenorhabditis elegans

Recent work in Caenorhabditis elegans has shown that restriction of glucose metabolism extends life span by primarily increasing oxidative stress to exert an ultimately increased resistance against oxidative stress, a process called (mito)hormesis.
Publicat de health victorro la 03:54 0 comentarii
Etichete: calorie, effects, organism
Research history
In 1934, Mary Crowell and Clive McCay of Cornell University observed that laboratory rats fed a severely reduced calorie diet while maintaining vital nutrient levels resulted in life spans of up to twice as long as otherwise expected. These findings were explored in detail by a series of experiments with mice conducted by Roy Walford and his student Richard Weindruch. In 1986, Weindruch reported that restricting the calorie intake of laboratory mice proportionally increased their life span compared to a group of mice with a normal diet. The calorie-restricted mice also maintained youthful appearances and activity levels longer and showed delays in age-related diseases. The results of the many experiments by Walford and Weindruch were summarized in their book The Retardation of Aging and Disease by Dietary Restriction (1988) (ISBN 0-398-05496-7).

The findings have since been accepted and generalized to a range of other animals. Researchers are investigating the possibility of parallel physiological links in humans. In the meantime, many people have independently adopted the practice of calorie restriction in some form.
In 1934, Mary Crowell and Clive McCay of Cornell University observed that laboratory rats fed a severely reduced calorie diet while maintaining vital nutrient levels resulted in life spans of up to twice as long as otherwise expected. These findings were explored in detail by a series of experiments with mice conducted by Roy Walford and his student Richard Weindruch. In 1986, Weindruch reported that restricting the calorie intake of laboratory mice proportionally increased their life span compared to a group of mice with a normal diet. The calorie-restricted mice also maintained youthful appearances and activity levels longer and showed delays in age-related diseases. The results of the many experiments by Walford and Weindruch were summarized in their book The Retardation of Aging and Disease by Dietary Restriction (1988) (ISBN 0-398-05496-7).

The findings have since been accepted and generalized to a range of other animals. Researchers are investigating the possibility of parallel physiological links in humans. In the meantime, many people have independently adopted the practice of calorie restriction in some form.

Trials were set up at Washington University in 2002 and involved about thirty participants. Dr. Luigi Fontana, clinical investigator, says CR practitioners seem to be aging more slowly than the rest of us. "Take systolic blood pressure," he says. "Usually, that rises with age reliably, partly because the arteries are hardening. In my group, mean age is 55, and mean systolic blood pressure is 110: that’s at the level of a 20-year-old."

A study conducted by the Salk Institute for Biological Studies and published in the journal Nature in May 2007 determined that the gene PHA-4 is responsible for the longevity behind calorie restriction in animals, 'with similar results expected in humans'.[10] The discovery has given hope to the synthesising of future drugs to increase the human lifespan by simulating the effects of calorie restriction. However, MIT biologist Leonard Guarente cautioned that "(treatment) won't be a substitute for a healthy lifestyle. You'll still need to go to the gym".[11]
Publicat de health victorro la 03:53 0 comentarii
Etichete: calorie, history, Research
Negative effects on humans
Underweight

Being on a CR diet can lead to an individual becoming underweight. One study has shown that having a BMI lower than 18 is associated with significantly increased mortality from noncancer, non−cardiovascular disease causes. The results were the same when not for accounting those who were underweight because they might have been already sick or were smokers. However, the study focused solely on BMI and did not look specifically at diet.[7]

[edit] Muscular atrophy

When in Starvation mode the body burns lean tissue and muscle in order to conserve fat reserves.[8] That combined with low protein/carbohydrate intake can result in Muscular atrophy which leads to lower quality of life.

[edit] Lack of essential nutrients

When reducing calorie intake some may also reduce the intake of essential nutrients. Especially fat-soluble vitamins, which require fat for proper absorption and others generally associated with high calorie foods, like nuts, meat and dairy products.

[edit] Abnormal hair growth

When undernourished the body slows the growth rate of hair and nails.[9]
Publicat de health victorro la 03:50 0 comentarii
Etichete: calorie, effects, humans
Positive effects on humans
In human subjects, CR has been shown to lower cholesterol, fasting glucose, and blood pressure.[citation needed] In CR, energy intake is minimized, but sufficient quantities of vitamins, minerals and other important nutrients must be eaten.

A small-scale study in the US at the Washington University School of Medicine in St. Louis studied the effects following a calorie-restricted diet of 10-25% less calorie intake than the average Western diet. Body mass index (BMI) was significantly lower in the calorie-restricted group when compared with the matched group; 19.6 compared with 25.9. The BMI values for the comparison group are similar to the mean BMI values for middle-aged people in the US.[2]

All those on calorie-restricted diets experienced reductions in BMI after starting their diet. Their BMIs decreased from an average of 24 (range of 29.6 to 19.4) to an average of 19.5 (range of 22.8 to 16.5) over the course of their dieting (3-15 years). Nearly all the decrease in BMI occurred in the first year of dieting. It was found that the average total cholesterol and LDL (bad) cholesterol levels for calorie-restricted individuals were the equivalent of those found in the lowest 10% of normal people in their age group. It was found that the average HDL (good) cholesterol levels for calorie-restricted individuals were very high—in the 85th to 90th percentile range for normal middle-aged US men. These positive changes in calorie-restricted individuals were found to occur mainly in the first year of dieting. [2]

"The calorie-restricted group also fared much better than the control group in terms of average blood pressure (100/60 vs. 130/80 mm Hg), fasting glucose, fasting insulin (65% reduction), body mass index (19.6 ± 1.9 vs. 25.9 ± 3.2 kg/m2), body fat percentage (8.7% ± 7% vs. 24% ± 8%), C-reactive protein, carotid IMT (40% reduction), and platelet-derived growth factor AB."[3]

It was found that the calorie-restricted group had remarkably low triglyceride levels. In fact, they were as low as the lowest 5% of Americans in their 20s. This is more remarkable when it is noted that the calorie-restricted individuals were actually aged between 35 and 82 years. Both systolic and diastolic blood pressure levels in calorie-restricted group were remarkably low, about 100/60, values normally found in 10-year-old children. Fasting plasma insulin concentration was 65% lower and fasting plasma glucose concentration was also significantly lower in the calorie-restricted group when compared with the comparison group." The comparison group's statistics aligned approximately with the US national average on the dimensions considered.[4] Fasting plasma insulin levels[5] and fasting plasma glucose levels[6] are used as tests to predict diabetes. "[The researchers also] found that excessive calorie restriction causes malnutrition and can lead to anemia, muscle wasting, weakness, dizziness, lethargy, fatigue, nausea, diarrhea, constipation, gallstones, irritability and depression. The study was published in the March 2007 issue of the Journal of American Medical Association."[2]

While compelling, these studies used borderline overweight (BMI>25) subjects as controls, which is the average in some countries but not in others. It remains unclear whether the same effects would also be observed if non-overweight subjects were used as controls.

• Added on: Mar 13th, 2009
• Country: Romania
• Language: English

• Author: rorac2009
• Listed in: Health Medicine
• Tags: research history effects of cr on different organisms