Which is more effective: Intermittent Fasting or Calorie Restriction?

Is the key to living a longer, healthier life found in meal skipping or making smarter food choices? A groundbreaking study has finally shed light on the debate between calorie restriction and intermittent fasting for longevity. The results may catch you off guard...

Overview

• Restricting calories surpasses intermittent fasting for longevity, as mice on a 60% reduced-calorie diet lived 36% longer compared to those on unrestricted diets.
• Genetic resilience plays a crucial role in lifespan; mice maintaining weight and immune health under caloric restriction lived the longest.
• Weight loss may not lead to longevity, as losing weight during calorie restriction was linked to shorter lifespans, challenging conventional views on metabolic health indicators.

What We Know About Calories and Longevity

Research indicates that animals consuming less food or eating less frequently tend to live healthier and longer lives. There is also evidence showing that calorie restriction enhances people's longevity, too. However, it remains uncertain whether calorie restriction or intermittent fasting is more beneficial for extending lifespan.

In one of the most significant longevity studies to date, researchers discovered that calorie restriction was more effective. Nevertheless, the scenario is not straightforward because—brace yourself—diet surprisingly isn't the primary factor influencing longevity at all.

For nearly a century, studies in laboratories consistently demonstrated that calorie restriction (CR) prolongs lifespan in various species. Yet, let's be honest, few of us wish to be hungry all the time! That's simply not a sustainable way to live.

Unsurprisingly, researchers turned to exploring more tolerable methods of dietary restriction. Luckily, these approaches still demonstrate health and lifespan benefits in animal studies on both time-restricted feeding (calorie restriction) and intermittent fasting (IF). The former restricts daily intake to a four to 12-hour window, while the latter limits food consumption to one or several days per week.

In studies on rodents, intermittent fasting extends life and shields against obesity, heart disease, high blood pressure, diabetes, and brain disorders. These advantages can occur even without an overall decrease in calories.

However, there is limited data on the distinctions between calorie restriction and intermittent fasting in terms of healthy aging and longevity, and individual responses to these diets differ.

In mice and non-human primates, the effect is influenced by gender, body size, body composition, and genetics. Meanwhile, human studies have been brief and focused on alterations in body weight, fat mass, energy metabolism, and risks related to heart health.

Inadequate knowledge makes it challenging to anticipate how individuals will react to dietary restrictions, so identifying specific biological indicators could assist in tailoring the diet to individual requirements.

To this end, researchers at The Jackson Laboratory in Maine conducted an extensive and pivotal experiment on mice.

Severe Calorie Restriction Extends Life Most

They utilized 960 female mice, each genetically distinct to better represent the genetic diversity of the human population. Researchers allocated each mouse to one of the following five diets:

• Unrestricted - eat as much as they want
• Calorie restriction - 60% of their usual intake each day
• Calorie restriction - 80% of their usual intake each day
• Intermittent fasting - fasted on one day a week, unrestricted on other days
• Intermittent fasting - fasted on two consecutive days, unrestricted on other days

Subsequently, they monitored the mice throughout their lives with periodic blood tests and comprehensive overall health assessments. Here is the average lifespan of each group:

• Unrestricted - 25 months
• Intermittent fasting - 28 months (combination of both fasting regimens outlined above)
• Calorie restriction 80% - 30 months
• Calorie restriction 60% - 34 months

The clear winner was the group that consumed the least. The nine-month difference between this group and those allowed to eat as much as they desired is significant in a species with a lifespan of less than three years.

Explore more about the health benefits of intermittent fasting here.

There was also another intriguing discovery.

The Importance of Resilience

Diets extremely low in calories extended lifespan irrespective of body fat and glucose levels — typically considered and focused on as indicators of metabolic health and aging in human studies.

Furthermore, the mice that lived the longest shed the least weight despite consuming less. They maintained their body weight, body fat percentage, and immune cell health, while those that lost the most weight tended to experience low energy, compromised immune and reproductive systems, and shorter lifespans.

Gary Churchill, the senior author of the study published in the journal Nature in October, explains: “Our study really emphasizes the significance of resilience. The most resilient animals maintain their weight even under stress and caloric restriction, and they are the ones that live the longest.”

Exciting news, isn't it? Well, kind of...

Genetics Played a Key Role

A closer look at the research reveals that mice consuming the fewest calories had lifespans ranging from a few months to four and a half years. How is this possible? Researchers attributed this wide range in lifespan within each group to genetic factors. For instance, genetic factors had a far greater influence on lifespan than diets, underscoring how unidentified underlying genetic characteristics play a major role in how such diets impact future health.

Regrettably, this study implies that you need to hit the genetic jackpot to hit the century mark, as Professor Churchill succinctly puts it. “If you want to live a long time…what you want is a very old grandmother.”

However, other studies have suggested that your diet and lifestyle can override your genetic code when it comes to health and longevity. Furthermore, it also appears that researchers focusing on human aging are looking in the wrong direction.

Cut Calories Not Weight

Factors affecting metabolism such as weight, body fat percentage, body temperature, and blood glucose levels, are conventionally cited to explain why certain diets extend life. However, the findings from the Jackson Lab raise doubts on this. Immune system health and traits linked to red blood cells were more evidently associated with lifespan.

“While caloric restriction generally benefits lifespan, our data indicate that losing weight during caloric restriction actually harms lifespan,” Professor Churchill elaborated. “Therefore, when we observe human trials of longevity drugs where individuals are losing weight and have improved metabolic profiles, it turns out that this might not be a good indicator of their future lifespan after all.”

These results do not diminish the importance of diet, as Professor Churchill emphasizes:

“If you aim to live a long life, there are controllable factors within your lifetime such as diet. A more moderate level of calorie restriction might be the way to strike a balance between long-term health and lifespan.”

Summary

A groundbreaking study from The Jackson Laboratory compared the impacts of calorie restriction (CR) and intermittent fasting (IF) on longevity using genetically diverse mice. Findings revealed that mice on severe calorie restriction lived notably longer than those on intermittent fasting or unrestricted diets, with a 60% calorie reduction extending lifespan by 36%. Interestingly, the study unveiled that resilience to calorie restriction — maintaining weight and immune health — played a more significant role in longevity than weight loss or metabolic markers. Ultimately, genetics emerged as the most critical factor influencing lifespan, challenging traditional beliefs about aging and diet.

Frequently Asked Questions

What is calorie restriction (CR)?

Calorie restriction involves reducing daily caloric intake, often by 20–40%, while maintaining essential nutrient intake.

What is intermittent fasting (IF)?

Intermittent fasting alternates periods of eating and fasting, such as time-restricted feeding or fasting on certain days of the week.

Why does calorie restriction work better than intermittent fasting?

The study suggests that calorie restriction consistently supports longevity by improving resilience and immune health, rather than focusing on weight loss or metabolic markers.

Does intermittent fasting still have benefits?

Yes, intermittent fasting can enhance metabolic health and reduce risks of obesity, diabetes, and cardiovascular diseases, even without significant calorie reduction.

Is genetics more important than diet for longevity?

According to the study, genetics plays a significant role in determining how diets impact lifespan, making it a crucial factor alongside diet and lifestyle.