Tuesday, August 28, 2012

Dietary Restriction: Impact On Health And Longevity

Studies of food plans that show reductions in disease, or markers of disease, often see subjects decreasing their caloric intake, sometimes resulting in weight loss. That leads to murky results. Was it eating fewer carbohydrates that improved blood glucose? Or was it the weight loss? Or just eating less?

Results are statistically adjusted for these and other variables to better understand the independent effect of dietary components, because it's known that merely reducing calories, or reducing weight, however that's achieved, reduces disease risk.

Thus, I've been reading:

Impact Of Caloric And Dietary Restriction Regimens On Markers Of Health And Longevity In Humans And Animals: A Summary Of Available Findings, Nutrition Journal, October 2011

It looked at:
  • Caloric restriction (CR) - cutting intake from 20% to 40% of ad libitum intake (an intake a person would engage in if they had no restrictions).
And alternatives to CR:
  • Dietary restriction (DR) - restriction of one or more dietary components (typically carbs, protein, or fat) with minimal to no reduction in total caloric intake.
  • Alternate-day fasting (ADF) - two interchanging days: one day food is consumed ad libitum (sometimes equaling twice the normal intake), the next day food is reduced or withheld altogether.
  • Caloric restriction combined with exercise (CE)
  • Religious fasting - focused on Islamic Ramadan, 3 fasting periods of Christianity (Nativity, Lent, and the Assumption), and the Biblical-based Daniel Fast.

Let's just look at that first item, CR, or cutting calories:

Caloric Restriction In Animals

"CR improves cardiovascular health. ... CR reduces levels of triglyceride, phospholipid, and total and low density lipoprotein (LDL) cholesterol. CR also increases HDL2b levels and reduces inflammatory markers such as TNF-α, IL-6, C-reactive protein, and NF-κB. ... Several studies have noted significant declines in both blood pressure and heart rate. Other work has noted cardioprotective alterations in gene expression."

"CR appears to improve glucoregulatory function and insulin sensitivity. ... Several studies have observed a decrease in fasting blood glucose and insulin."

"Reductions in markers of oxidative stress such as hydrogen peroxide, protein carbonyls, and nitrotyrosine have been noted."

"CR has been shown to lower brain-reactive antibodies and to reduce T-lymphocyte proliferation."

"CR has been reported to reduce tumor growth, decrease body weight, reduce sarcopenia, maintain neural/cognitive function, and improve immune function."

"Collectively, these changes have been associated with an increase in lifespan in many studies involving animals."

Caloric Restriction In Humans

"CR improves cardiovascular and glucoregulatory health. ... CR may reduce the risk of cardiovascular disease by lowering total cholesterol, triglycerides, blood pressure, and carotid intima-media thickness. CR also has been shown to attenuate the age-related decline in diastolic function."

"Regarding glucoregulatory health, circulating insulin and glucose levels decrease - while insulin sensitivity increases."

"CR has also been shown to attenuate oxidative stress, a condition thought to contribute to aging and disease."

"Enhanced verbal memory performance has been reported in elderly individuals."
I mean, this is a spectacular list of health variables. It's like listening to an infomercial for a new drug but without the rushed list of side effects at the end.

So, merely eating less, about 400 fewer calories a day (20% of 2000 calories is 400 calories) has enormous health benefits. But is it realistic? It doesn't appear so, given the prevalence of obesity. What about alternatives to CR? Can these same benefits be achieved by, say, restricting carbs or protein, but keeping calories unchanged? Or by incorporating just a few days where we eat less? Maybe exercise a little instead of going full-on CR? Yes, it looks like some of these alternatives work.

Let's look at dietary restriction (DR) first. I'll come right out and say it here too, restricting carbs and fat didn't work, but restricting protein did.

This was one in a series of 4 posts:
Thanks again to healthy-longevity and his or her blog, where I found this study.


Bix said...

I may as well post this:

Severe Diet Doesn’t Prolong Life, Study of Monkeys Concludes, NYTs, August 29

"Monkeys that ate less did not live any longer than those that ate normally."

"The causes of death — cancer, heart disease — were the same in both the underfed and the normally fed monkeys."

Bix said...

The causes of death were the same, but the monkeys that ate less were still healthier, still experienced a better quality-of-life. I'll be posting a little more about this new study.