There has been a lot of interest in whether restricting calorie intake can slow down the aging process and extend lifespan. Calorie restriction (CR), sometimes referred to as dietary restriction, means reducing food intake while avoiding malnutrition. In animal studies, CR has been shown to increase maximum lifespan and delay the onset of age-related diseases. Some researchers believe that CR may also have anti-aging effects in humans. This article will review the evidence on whether eating less can slow aging and increase longevity.
Animal studies on calorie restriction
CR studies in animals date back to the 1930s when researchers found that severely restricting the diets of rodents could significantly increase their lifespans (1). Since then, hundreds of animal studies have confirmed the anti-aging effects of CR in species ranging from worms and flies to mice and non-human primates (2).
Some key findings from animal research include:
- CR extends maximum lifespan in mice and rats by up to 50% (3).
- It delays the onset of age-related diseases like cancer, diabetes, and cardiovascular disease (4).
- CR improves healthspan by preserving muscle mass and motor function into old age (5).
- The metabolic, hormonal, and physiological changes induced by CR may slow aging processes in the body (6).
Overall, the animal data strongly supports CR as an intervention that can increase both average and maximum lifespan. However, the degree of restriction required is quite severe, typically reducing calorie intake by 30-60% below ad libitum feeding levels.
Mechanisms of calorie restriction
There are several key mechanisms proposed to explain how CR promotes longevity (7):
- Reduced metabolic rate – CR lowers metabolic rate and oxidative stress generated by mitochondrial respiration.
- Enhanced repair – CR upregulates cellular repair processes and removes damaged molecules.
- Improved insulin sensitivity – CR enhances insulin sensitivity and reduces chronic inflammation.
- Altered signaling – CR induces epigenetic changes that alter the expression of pro-longevity genes.
The reduction in metabolic processes and oxidative damage is thought to be a key driver of CR’s protective effects. However, the specific molecular pathways involved are still not fully understood.
Does calorie restriction work in humans?
There is considerable debate over whether the robust longevity effects of CR demonstrated in animal studies translate to humans. Conducting tightly controlled CR experiments in humans over decades is not feasible. However, researchers have sought evidence from various human studies:
Bio-markers of aging
Several short-term human CR studies lasting 1-2 years have found that CR causes changes similar to those observed with CR in animals, including (8):
- Lowered metabolic rate and body temperature
- Improved insulin sensitivity and reduced inflammation
- Increased autophagy (cellular repair)
These bio-marker changes suggest CR induces a more ‘youthful’ profile in the body. However, it is not known if these changes would actually impact the rate of human aging over the long-term.
Genetic studies
Humans with mutations in the growth hormone/IGF-1 axis that lead to reduced IGF-1 levels have been found to have increased maximal lifespans (9). This mutation somewhat mimics the effects of CR, suggesting CR could also extend human lifespan. However, the mutation has many deleterious developmental effects, making it different than CR.
Observational studies
Some observational data links eating less with longevity. For example, Okinawans and adherents to calorie-restricting diets like the CRON diet generally have high percentages of centenarians (10). Members of the Calorie Restriction Society who practice 30% CR have much lower rates of age-related disease compared to the general population (11).
However, observational studies cannot prove CR is directly responsible for increased lifespan due to potential confounding factors. CR adherents may share other healthy behaviors that contribute to their longevity.
Clinical trials
There are currently two ongoing long-term clinical trials directly testing the effects of CR in humans – the CALERIE trial in the USA and the CARE trial in Europe (12, 13). However, results will not be available for at least another decade. In the meantime, we must rely on the available evidence outlined above.
Table summarizing key evidence on calorie restriction and aging
| Evidence Source | Key Findings |
|---|---|
| Animal studies | CR consistently extends lifespan and delays age-related disease in diverse species. |
| Mechanistic studies | CR induces metabolic, hormonal, and epigenetic changes that slow aging processes. |
| Human biomarker studies | Short-term CR causes beneficial changes in biomarkers that resemble CR animals. |
| Genetic studies | Humans with mutations mimicking CR effects have increased longevity. |
| Observational studies | Groups voluntarily restricting calories have higher percentages of centenarians. |
| Clinical trials | Ongoing trials will directly test if CR extends human lifespan. |
Is severe calorie restriction feasible and healthy for humans?
While the evidence for CR is compelling, implementing very restrictive regimens long-term may not be feasible or necessarily advisable for most people. Some major considerations include:
- Severe CR below 50% of normal intake risks malnutrition and loss of lean tissue like muscle and bone over time.
- Extreme restriction is difficult to adhere to for decades due to hunger and psychological challenges.
- Metabolic adaptations to severe CR include hypothermia, lower libido, and amenorrhea in women.
- Moderate CR may achieve a good balance between longevity effects and quality of life.
For these reasons, many experts recommend a moderate CR regimen of around 10-25% reduction from a normal diet, along with maintaining proper nutrition (14). This level of restriction is more feasible for long-term compliance while still activating many of the protective mechanisms of CR.
Other potential anti-aging diets
Besides strict calorie reduction, some other dietary interventions have shown promise for anti-aging and longevity benefits:
Intermittent fasting
Intermittent fasting cycles periods of fasting and normal eating, often on a daily or weekly schedule (15). Studies show intermittent fasting activates similar pathways as CR and may provide some of the same anti-aging effects if it leads to an overall reduction in average calorie intake (16).
Protein restriction
Restricting protein intake to 0.8-1.0 g/kg while maintaining normal calorie intake has extended lifespan in rodent studies (17). Lowering the percentage of calories from protein may be an alternative approach to CR for longevity.
Fasting-mimicking diets
These diets aim to mimic the physiological effects of fasting over 3-5 day cycles with specialized low protein, low calorie foods (18). Early human trials suggest they can activate regenerative pathways similarly to water-only fasting.
Conclusion
The preponderance of evidence from animal studies supports calorie restriction as one of the most robust interventions known to slow aging and extend healthy lifespan. However, the degree to which CR induces the same beneficial effects in humans remains an open question. While ongoing clinical trials will eventually provide direct data on CR and longevity, moderate CR regimens of 10-25% are likely a safe approach based on current knowledge. Other fasting-based diets may provide alternatives to strict CR for longevity. But further research is needed to optimize anti-aging dietary recommendations for humans.