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Not just what you eat, but when: Fasting improves mood and energy

Fasting for 14 hours per day can notably improve mood, energy, and reduce hunger levels, according to a new study led by researchers at King’s College London.

The study, which was presented at the European Nutrition Conference, is part of the largest UK community science project of its kind.

Restrictive eating window

Intermittent fasting involves limiting food intake to a specific time frame – in this case, ten hours – followed by a 14-hour fast. For example, if you begin eating at 9am, you should finish eating by 7pm. 

While some advocates suggest restrictive eating windows as low as six hours, the new research shows that eating within a less restrictive window of ten hours is still associated with significant health benefits, including positive changes in mood, energy, and hunger.

Consistency matters

An important highlight of the study is the emphasis on consistency. Dr. Sarah Berry noted that this is the largest study outside of a tightly controlled clinic to show that intermittent fasting can improve your health in a real world setting. 

“What’s really exciting is that the findings show that you don’t have to be very restrictive to see positive results. A ten-hour eating window, which was manageable for most people, and improved mood, energy levels and hunger,” said Dr. Berry.

“We found for the first time that those who practiced time-restricted eating, but were not consistent day to day, did not have the same positive health effects as those who were dedicated every day. ”  

Focus of the study 

The study involved 37,545 individuals using the ZOE Health app, undergoing a three-week core intervention period. 

Initially, participants ate normally for a week, followed by a two-week period of the ten-hour eating window. A large number of participants (over 36,000) chose to continue beyond the initial weeks. 

Those classified as highly engaged were predominantly women with an average age of 60 and a BMI of 25.6. This group showed even greater health benefits, especially if they had a longer eating window before the intervention.

Study significance 

“This study adds to the growing body of evidence showing the importance of how you eat. The health impact of food is not just what you eat but the time at which you choose to consume your meals, and eating window is an important dietary behavior that can be beneficial for health,” said Dr. Kate Bermingham. 

The findings show that we don’t need to be eating all the time, and that many people feel satiated and even lose weight if they restrict their food to a ten-hour window, she added. 

The research offers a new perspective on intermittent fasting, suggesting that a more flexible approach can be just as beneficial as more restrictive practices, with the added advantage of being easier to maintain for most people.

The study has not yet undergone the peer review process required for publication in a scientific journal.

Intermittent fasting

Intermittent fasting (IF) is a dietary approach that cycles between periods of fasting and eating. It has gained popularity in recent years due to its simplicity and potential health benefits.

Types of IF

Time-restricted eating 

Time-restricted eating involves eating all your meals within a certain number of hours each day. The 16/8 method (fasting for 16 hours and eating within an 8-hour window) is one of the most popular.

5:2 diet

Eating normally for five days of the week and restricting calorie intake to 500–600 calories on the other two, non-consecutive days.

Alternate-day fasting

Alternating between normal eating days and fasting or severely reduced calorie days.

Spontaneous meal skipping 

Skipping meals when convenient, without a structured plan.

Potential health benefits

Weight loss and body fat reduction

By reducing calorie intake and increasing fat burning, intermittent fasting can aid in weight loss.

Improved metabolic health

IF can improve various metabolic markers, such as blood sugar levels, blood pressure, and cholesterol levels.

Enhanced brain health

Some studies suggest fasting may benefit brain health and could potentially reduce the risk of neurodegenerative diseases.

Increased longevity

Research in animals has shown that IF can extend lifespan, although human studies are needed.

How it works

  • When fasting, the body switches to burning fat for energy, a process known as ketosis.
  • Fasting decreases insulin levels, which facilitates fat burning.
  • Fasting triggers autophagy, a process where cells repair themselves and remove damaged components.
  • Fasting changes the function of genes related to longevity and protection against disease.

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