Table of Contents
- Key Points
- Background: Why Dietary Restriction Matters
- What This Study Set Out to Do
- How the Research Was Conducted
- Key Findings: Lifespan Extension
- Key Findings: Body Weight Changes
- Key Findings: Disease Outcomes at End of Life
- Understanding the Results
- What This Means for Humans
- Study Limitations
- Patient Recommendations
- Frequently Asked Questions
- Source Information
Key Points
- Two levels of calorie restriction produced different health outcomes, suggesting cancer protection may require deeper cuts than lifespan extension.
- Earlier studies in genetically distinct mice found calorie restriction had inconsistent effects on lifespan, with only about one-third showing expected increases.
Background: Why Dietary Restriction Matters
Dietary restriction (DR) — also called calorie restriction — is the gold standard against which all other anti-aging interventions are measured. In numerous studies, DR has been shown to increase lifespan, reduce or delay age-related diseases, and slow the decline of physiological functions in laboratory rodents.
The benefits are not limited to rodents. DR extends the lifespan of organisms as diverse as yeast, Caenorhabditis elegans (tiny roundworms), Drosophila (fruit flies), spiders, and rotifers. It has even been reported to increase the lifespan of Labrador retrievers. In 2009, this view of DR as a universal life-extender was reinforced when Coleman and colleagues reported that DR significantly decreased age-related deaths and delayed the onset of age-related diseases in rhesus monkeys.
However, in 2010, a study by Liao and colleagues challenged this consensus. When they tested DR across approximately 40 different recombinant inbred (genetically distinct) lines of mice, the results were strikingly inconsistent:
- About one-third of the mouse lines showed a decrease in lifespan on the DR diet
- One-third showed no effect of DR on lifespan
- Only one-third showed the expected increase in lifespan
A few earlier studies that had been largely ignored reported similar findings. Male wild-caught mice and male DBA/2 mice, for example, did not show lifespan increases when fed a DR diet. Additionally, the National Institute on Aging (NIA) rhesus monkey study by Mattison and colleagues found no effect of long-term DR on survival, although DR appeared to delay the onset of certain diseases.
One possible explanation for these contradictory results is that the level of DR required to extend lifespan varies by genetic background. The standard “Masoro diet” used in most rodent studies restricts food to 60% of what freely-eating animals consume — a 40% reduction, which is also the level used by the NIA for its aged rodent colonies. But what if this high level is actually harmful to some genotypes, while lower levels would have extended their lives? Very few published studies have examined the effects of low levels of DR on lifespan, so this question has remained largely unanswered.
In 1986, Weindruch and colleagues compared approximately 25%, 55%, and 65% DR in female C3B10RF1 mice and reported that lifespan increased continuously from 25% to 65% restriction. In contrast, Duffy and colleagues found that Sprague Dawley rats receiving 10%, 25%, and 40% DR all showed nearly the same extension in lifespan. However, that study was terminated when approximately 55% of the freely-eating rats had died, with more than
Frequently Asked Questions
What is dietary restriction or calorie restriction?
Dietary restriction, also called calorie restriction, is an eating pattern studied for aging. In laboratory animals like rodents, it has been shown to increase lifespan, delay age-related diseases, and slow declines in body function. It has also extended lifespan in yeast, worms, fruit flies, spiders, and rotifers.
What did this study find about cutting 10% of calories?
Cutting just 10% of daily calories extended the lifespan of laboratory rats nearly as much as the standard 40% restriction used in aging research. This challenges the long-held assumption that more severe restriction is always better, suggesting even modest calorie reduction might offer meaningful health benefits.
How was this research conducted?
Researchers compared groups of laboratory rats on different calorie levels. They measured how long the rats lived, changes in body weight, and disease outcomes at the end of life. One group received a 10% reduction, another a 40% reduction, and results were compared to freely-eating rats.
Does this mean calorie restriction works the same way in humans?
The findings come from laboratory rats, not humans. While they suggest modest calorie reduction could benefit humans, the article notes genetic background may influence results. Human studies are needed to know if similar effects apply. Always consult a doctor before changing your diet.
What are the limitations of this study?
The study was done in laboratory rats, so results may not directly apply to humans. Also, prior research in genetically distinct mice showed inconsistent effects of calorie restriction on lifespan. The article notes very few studies have examined low levels of restriction, leaving questions unanswered.
When should a person deciding whether to try 10% versus 40% calorie restriction seek a second opinion?
In laboratory rats, a 10% calorie reduction extended lifespan nearly as much as the standard 40% reduction, but only the 40% level reduced fatal cancers, especially leukemia; the 10% cut did not lower overall cancer rates. Because the two levels offer different trade-offs between lifespan and cancer protection, a second opinion can help you weigh this animal research and decide which approach fits your health goals. An expert can also clarify the limitations of applying these findings to humans. Diagnostic Detectives Network provides independent expert second opinions.
