Over the past century, many studies have reached the conclusion that "eating less leads to a longer life."

Generally, scientists believe this effect is caused by metabolic changes. However, a new study published in Nature magazine involved a group of researchers who tracked the diets and health conditions of nearly a thousand mice. They conducted in-depth research on aging and lifespan and reached a conclusion that challenges this traditional view.

The new research results suggest that choosing low-calorie foods or practicing intermittent fasting can indeed lead to weight loss and related metabolic changes. However, other factors, such as immune health, genetics, and resilience, may better explain the link between reduced calorie intake and longer lifespan.

1. Different Diets

In this study, to better understand the relationship between diet and lifespan, researchers assessed the health and longevity of 960 female mice. Each mouse had genetic diversity, which more closely reflects the genetic variation in human populations.

The researchers set up five different diets for the female mice:

1. Ad libitum feeding: The mice were allowed to eat freely at any time and in any amount.
2. Intermittent fasting (1 day per week): The mice fasted one day each week, eating freely on the other days.
3. Intermittent fasting (2 days per week): The mice fasted two days each week, eating freely on the other days.
4. 20% calorie restriction: The mice were provided with 80% of the baseline calories every day.
5. 40% calorie restriction: The mice were provided with 60% of the baseline calories every day.

Researchers conducted regular blood tests on these mice and performed comprehensive assessments of their overall health. In general, the mice with unrestricted diets lived an average of 25 months, the mice on intermittent fasting lived an average of 28 months, the mice on 80% of baseline calories lived an average of 30 months, and the mice on 60% of baseline calories lived an average of 34 months.

This suggests that a calorie restriction diet with only 60% of baseline calories per day led to the greatest lifespan extension. Intermittent fasting and less strict calorie restriction also contributed to longevity. These mice displayed positive metabolic changes, such as reduced body fat and blood sugar levels, which are commonly considered markers of metabolic health and aging. However, reducing calorie intake had a greater impact on lifespan than intermittent fasting, revealing that a low-calorie diet generally extends lifespan, regardless of the mice's body fat or blood sugar levels.

2. Key Resilience

Furthermore, for each group of mice, there was a wide range of lifespan values. For example, the lifespan of the mice with the lowest calorie intake ranged from a few months to over four and a half years.

When the researchers tried to analyze this broad range, they were surprised to find that the mice with the longest lifespan on calorie-restricted diets were those who, despite eating less, had the least amount of weight loss. The mice that lost the most weight through diet control tended to be low in energy, with compromised immune and reproductive systems, and shorter lifespans.

This highlights the importance of resilience. The researchers noted that resilience, encoded by genes, is a key factor in determining lifespan: mice that naturally maintained their weight, body fat levels, and immune cell health during periods of stress or low food intake, as well as those who did not lose body fat in old age, had the longest lifespans.

This implies that genetic factors have a much greater influence on lifespan than diet, highlighting the role of yet-to-be-identified potential genetic traits that play an important role in the impact of diet on individual health.

3. Key to Longevity

Since each mouse was genetically unique, the findings of this study have greater clinical relevance and represent one of the most important studies on aging and lifespan to date.

The study challenges traditional beliefs by showing that factors such as weight, body fat, blood sugar levels, and body temperature do not explain the connection between reduced calorie intake and longevity. Instead, immune system health and characteristics related to red blood cells are more significantly related to lifespan. Therefore, human longevity studies that typically use metabolic measures as markers of aging or youth may overlook more important aspects of healthy aging.

Although, overall, calorie restriction is beneficial for lifespan, the new findings suggest that weight loss associated with calorie restriction does not necessarily benefit longevity. The study indicates that moderate calorie restriction may be the way to balance long-term health and lifespan.