All you need to know about calorie restriction for weight loss, and longevity

The optimal level of calorie restriction requires making broader lifestyle choices such as consuming a protein-rich diet, prioritizing nutrient-dense and low-calorie foods and engaging in regular physical activity. (Photo by Maarten Van Den via Pexels)

Calorie restriction is a dietary intervention popularly followed by individuals who aim to lose body fat by reducing daily caloric intake without malnutrition or deprivation of essential nutrients. It’s an exciting and complex area of nutritional science that has gained attention due to its link to weight loss and various health benefits, such as the decreased risk of age-related diseases and lifespan extension.

However, it’s essential to point out the potential side effects of calorie restriction and the need for a balanced framework to avoid poor health outcomes. In that spirit, here's a look at the published material on the benefits and possible side effects of calorie restriction, to help understand it better and to see how it can be applied for desired longevity and weight loss results.

What is calorie restriction?

The inception of the calorie restriction diet traces back to laboratory studies conducted during the 1930s on yeast, worms, and mice, which revealed an extension of lifespan with reduced caloric intake. Researchers noted that rats with significantly reduced food intake lived longer than those fed ad libitum. Over time, there is suggestive evidence of this effect in humans as well.

As per a study in the Journal of Nutrition, since the early 20th century, the idea of calorie restriction has been predicated on the notion that by reducing the caloric intake to 60-80 percent of one’s requirement while sustaining sufficient nutrient supply, one can enhance their lifespan and general health.

So, for example, if your energy requirement for maintaining your current body weight is 2000 kcal, then consuming calories anywhere between 1200-1600 kcal daily would be defined as a calorie-restricted diet.

Benefits of consuming fewer calories

As per the article ‘The Hallmarks of Aging’ published in the peer-reviewed journal Cell, many of the health benefits of calorie restriction are related to ageing and longevity. From yeast to primates, research in various species has documented that calorie restriction can extend lifespan and delay the onset of age-related degeneration and diseases.

The benefits of calorie restriction on slowing ageing, as per a literature review published in The Journal of Physiology, transpires through various mechanisms such as reduction in oxidative stress, enhancing the production and functioning of powerhouses in our body known as the mitochondria that convert the food we consume and oxygen that we breathe into energy, a phenomenon known as improved metabolic efficiency and also promoting the body’s self-cleaning process known as autophagy.

Apart from longevity, as per an article published in Cell Metabolism, calorie restriction also has potential neuroprotective effects. In several animal models, it has slowed the progression of neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

Moreover, several studies in humans, including the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE) trial, have demonstrated the beneficial effects of calorie restriction on biomarkers of ageing, cardiovascular health, such as healthy reduction in blood pressure and improvement in lipid profile and metabolic risk factors such as reduction in levels of c-reactive protein (CRP), tumour necrosis factor-alpha (TNF-α), homocysteine and insulin levels.

Some research also demonstrates that calorie restriction can improve gut microbiota diversity, linked to several health benefits such as improved digestive health, nutrient absorption and immunity.

Potential Side Effects of Calorie Restriction

While the benefits of calorie restriction are noteworthy, when taken to the extreme without a mindful and proactive approach, calorie restriction has potential drawbacks. When approached incorrectly, it can cause malnutrition and negatively impact the health of the skeleton and muscles. A bone density and muscle mass reduction over time can progress into a degenerative condition known as osteoporosis and a reduction in physical strength, causing frailty.

As per a landmark study conducted by Ancel Keys and colleagues entitled The Biology of Human Starvation, extreme calorie restriction can also have a detrimental psychological impact as it disrupts our balance of ghrelin and leptin hormones that also control hunger and satiety; thus, severe caloric restriction will cause us to be constantly starving and feeling miserable throughout the day. This chronic hunger and preoccupation with food can cause bad mood swings, declined cognitive function and eating disorders.

Other side effects include hormonal imbalances, such as in women causing amenorrhea (the absence of menstruation), and decreased testosterone levels in men.

When done right, calorie restriction can reduce oxidative stress, improve metabolism and slow ageing. (Photo by Skylar Kang via Pexels)

Approaching Calorie Restriction Responsibly

The optimal level of calorie restriction that does not negatively impact health requires accommodating broader lifestyle choices such as consuming a protein-rich diet, prioritizing nutrient-dense and low-calorie foods and engaging in regular physical activity.

One fundamental formula you can use to ascertain your calorie needs; if you do not know your weight composition, the amount of fat and lean mass you carry within your current weight, is the Mifflin-St Jeor equation. However, if you know your composition of weight, then the formula that will give you more accurate results of your daily caloric needs is the Katch-McArdle equation.

Also read: Stick to these 5 healthy habits in your 30s to stay young forever

As a general rule of thumb, the less dangerous and well-studied caloric restriction level is between 20-40 percentage points of your daily caloric requirement. Additionally, as per a review of the literature on calorie restriction in humans published in Ageing Research Reviews, implementing a gradual reduction in calorie intake instead of a dramatic decrease can help the body adapt to the alterations and mitigate the potential adverse impact of the calorie-restriction diet. So the key here is not starvation but a modest reduction in calorie intake while ensuring adequate intake of essential nutrients.

Having said that, due to the enormous variation in individual needs based on body composition, physical activity levels, age, sex, goals, and temperament, seeking professional guidance is vital when starting a calorie restriction diet. A health coach or a registered dietician can provide personalized advice to warrant dietary adequacy personalized for you considering the above variables.

From a practical standpoint, periodic check-ups of various nutrients level and biomarkers are essential to monitoring your general health status, including changes in your body composition, psychological well-being and metabolic markers, thereby warranting that the benefits of calorie restriction outweigh the potential side effects. Most crucially, developing a positive relationship with food and listening to one’s body is necessary to avoid eating disorders.

While calorie restriction presents promising health and longevity benefits, it should be approached with caution and scientifically with proper calculation of calories, macronutrient composition, and optimal restriction pattern. Striking the right balance with professional guidance is crucial to leverage its benefits while minimizing potential risks.