Eat Less, Live Longer?
Wednesday, April 1st, 2009
Mary Crowell and Clive McCoy of Cornell University got the ball rolling on the link between dietary energy reduction and longer lifespan in 1934. They fed lab rats a severely calorie-reduced but otherwise nutritious regime and found their subjects lived up to twice normal lifespans.
Studies in 1986 by Walford and Weindruch shed light on possible parallels in humans. A small group of participants in a Washington University of St Louis project eating 10-25% less than the regular diet lowered their cholesterol, fasting blood glucose (used to predict diabetes) and blood pressure.
BMI went from an average of 24 to 19.5 over three to 15 years, though most BMI reduction took place in the first year of dieting. The most startling results were for blood tryglycerides (fats) which dropped as low as the lowest 5% of Americans in their twenties.
No long-term studies of significant dietary reduction in humans have taken place because of our long lifespans, so it’s too early to know for sure if the longevity enhancement seen in fruit flies and roundworms applies to us. However, a 2002 Washington University study showed dietary restriction greatly improved blood pressure. Arteries harden with age and blood pressure normally climbs with advancing years but this group with a mean age of 55 got theirs back to a youthful level.
There may be something in caloric reduction for a longer, healthier lifespan but it’s a fine line. Go too far and negative consequences like anemia, muscle wasting, gallstones and depression may derail a potential fountain of youth (March 2007 Journal of American Medical Association). Reducing your energy intake to 20 or 25 less than your requirements while maintaining adequate nutrients is risky, and quite frankly, a grind. Who wants to live longer if it means living on less than 2000 calories a day?
It seems plenty do, though academic research seems mainly aimed at understanding the nature of human metabolism and longevity. The Salk Institute for Biological Sciences identified the gene responsible (PHA-H) for the trick of living longer while eating less in animals and expect similar results for humans in the future.
At this stage, much of the debate is theoretical but (Mito)homesis leads the pack in explaining how energy-deprived rats live longer than their healthy counterparts on normal diets. Even obese rats put on calorie restriction live longer than normal rats, and calorie-restricted rats doing no exercise live longer than normally-fed rats that run on treadmills.
Where is the logic in this? It seems (Mito)homesis provides the best explanation in that calorie restriction creates a low-level biological stress that provokes a defense response via longevity genes.
It may be good old Darwinian medicine at work here. During famine, it’s likely that animals( small ones, anyway) avoid reproduction and upgrade their protective and repair mechanisms in order to outlive food shortages and to ensure reproductive capacity in the future.
Now this is all fine for yeast, rats, mice, fruit flies and chenorhabditis elegans (a 1 mm nematode) but it’s a big leap of faith to assume positive results in humans and adopt a semi-starvation regime. Muscle-wasting is not pleasant, and remember the heart is muscle.
Ray Walford, the prime 80s researcher in the field died of the disease calorie restriction is contra-indicated for - Amyotrophic Lateral Sclerosis (ALS) - sometimes called Lou Gehrig’s disease after the New York Yankees star who was diagnosed with it in 1939 at the peak of his career and died of it two years later. ALS is a neurodegenerative disease that affects the motor neurons; nerve cells that control voluntary movement. Perhaps Walford had been a long-term practitioner of his own research, with tragic results.
Reducing food energy intake in order to reduce excess bodyfat can reap a variety of health rewards that may in fact lead to a longer life but once a healthy weight is reached the risk of maintaining restricted calories for possible longevity improvement is just too great.
We need a wide variety and fair volume of foods to get all our required nutrients. Even weight-loss regimes that eliminate vital food groups like carbohydrates are potentially dangerous. Likewise, diets that vilify many healthy plant foods are of little use in the long term and may harm longevity.
I promised an overview of the GI Diet and will start with the American Diabetics Association’s view. They question the usefulness of GI for diabetics and reccomend the total amount and not the source of carbohydrate be given priority.
The Glycaemic Index(GI) goes something like this: Not all carbohydrate in all food acts alike when digested. Some is converted to glucose (blood sugar) more rapidly and a scale measuring the rate at which carbohydrate raises blood sugar compared to a mean of 50g of glucose is used. This gives foods a rating of one to 100. If a food raises blood glucose twice as high as 50g of glucose it ranks 100 on the GI, like potatoes. Not all potaoes - sweet potato, ironically rates lower than regular potatoes. Getting confused?
Ice Cream rates as a low GI food, probably because the fat in it delays glucose absorption. Ordinary table sugar rates moderately, almost smack bang in the middle at 55. The idea is to eliminate high GI foods in order to prevent a “rush” of insulin which may lead to declining insulin sensitivity and a pre-disposition to diabetes and overweight.
The GI ignores the real world and measures the effect of one food at a time, in standard amounts of carbohydrate. Remember, it’s how that food stacks up against 50g of glucose. Well, carrots are low in sugar and it would take several kilos of them to equate to 50g of glucose.
White rice is high GI, Basmati rice is not. Come on. The Glycaemic Index is complex and contradictory and not a realistic guide on how to eat. The sugar industry was an enthusiastic funder of early studies because white sugar performs well on the Index. Australian authorities and food companies are right behind GI as a means of attacking our obesity and diabetes problem but other countries aren’t so sure.
I don’t like reductivist science that scares people away from healthy, everyday foods like potatoes that have served humanity so well for so long. No potatoes, no Incas. The many varieties of “lumpers” eaten in huge quantities by the 18th and 19th century Irish made them the most energetic and sought-after labourers in the British Isles. An adult male ate 6 to 8 kilos a day (and little else) and their insulin and bodyfat levels were no doubt fine.
Professor Jenny Brand-Miller of Sydney University is a leading researcher, author and advocate of GI eating and was awarded the Clunies-Ross medal for services to Sugar, er Science and has based a succesful career on demonising one of humanity’s most nourishing foods. She and her colleagues have their knives out for potatoes; not to eat them but to destroy their reputation.
Eat a wide variety of plant foods regardless of how they rate against each other in the lab and the imaginations of reductivist scientists, and exercise and keep bodyfat levels down in order to live a longer healthy life.
