Time-restricted diets are programs that manipulate the timing of eating occasions using short-term fasts. This is targeted to improve body composition and overall health.

This is a fairly popular method of fasting in the dieting world. A notable and well-known version of this is perhaps the fasting from dawn to dusk observed by the Muslims during the holy month of Ramzan.  

The main difference between this type of diet from the others like Ketonic diets, Ornish diets etc. is that while the latter category focuses on what you eat, the former is only concerned about the duration of time at which you get to eat.

So time-restricted diets are not concerned about the calorie intake or type of food you eat as long you can confine your consumption time within the specified time restriction.

How Does Time-Restricted Fasting Work?

One of the reasons why this is so popular is its inherent ability to be customised as per your need along multiple dimensions like food choice, time of eating etc. It means that you do not have to follow a certain rigid method that someone else set.

An example is a time-based customisation. You may restrict your consumption window for 6 – 14 hrs. Say you choose an 8-hr window. This would mean that you are allowed to eat for an 8-hr continuous period as per your discretion. This may be from 5 PM to 1 AM (or any other 8-hr window of your choice). The rest of the time, you will not eat anything else. Now that part is also customisable.

Another one is food-based customization. This allows you to customize what you may eat/drink during the 16-hr window beyond your chosen consumption window. Ideally, people would choose to have only drinks that do not add any calories or sugars into the body like water, unsweetened tea/coffee etc. Drinking plenty of water is considered to be very important so as to remain sufficiently hydrated throughout the day.

Everyone is metabolically different. Rather than following someone else blindly on this, it is always better to consult your doctor and adopt a customized version of this diet that will suit the unique requirements of your body.

Now, let’s come to the main question.

How effective is this method of fasting in relation to weight loss or overall health improvement?

Let’s find out.

Benefits of Time-Restricted Fasting

1. Weight Loss

Well… duh! Of course, you want to knock some pounds off you. There are few other reasons why someone would put themselves through a diet. But let’s see what some studies say about this.

A review¹ (Rothschild et al., 2014) analysed the existing evidence-based on scientific studies regarding the correlation between time-restricted feeding and the risk of metabolic diseases. It found that data from human and animal studies did demonstrate a decrease in body weight (on a differential basis by case), concentrations of triglycerides, glucose and LDL (or ‘bad cholesterol’) when subjects went on time-restricted fasting. Additionally, they also noted an increase in HDL or ‘good cholesterol’.

A study² (Chung et al., 2016) on the effect of time-restricted feeding on postmenopausal obesity using mouse model was published in 2017. Data gathered from it supported the role of time-restricted feeding to improve metabolic health that was damaged due to obesity.

A study⁴ (Chaix et al., 2014) in mice was conducted to evaluate the effectiveness of time-restricted feeding against different diet types, eating patterns and existing obesity. These experiments revealed that Time-Restricted Feeding (TRF) efficiently protected against body weight gain when animals were subjected to diverse nutritional challenges and feeding schedules. Time-restricted feeding also promoted weight loss and efficient weight stabilization when used as a therapeutic intervention on pre-existing diet-induced obesity.

A study⁶ (Magnus et al., 2017) showed that time-restricted feeding on just weekdays (and no time restrictions on weekends) restricted weight gain in mice with high-fat diet-induced obesity.

2. Promotes Intestinal Health

A study³ (Ren et al., 2019) published in 2019 revealed that time-restricted feeding may have a protective effect against liver-related injury possibly through adjusting the gut microbiota. This was an investigation of time-restricted feeding at a surgical level.

3. Improves Heart Health

Time-Restricted feeding may protect against metabolic diseases and promote heart health.

A research⁵ (Megumi et al., 2012) was conducted to find if time-restricted feeding without a reduction in caloric intake prevents metabolic diseases in mice fed a high-fat diet. It confirmed the same and observed that time-restricted feeding resulted in a reduction in weight gain and improved hepatic glucose metabolism.

A study⁸ (Melkani & Panda, 2017) was conducted on the effect of time-restricted feeding on the prevention and treatment of cardio-metabolic disorders. Many cardio-metabolic benefits were found to accrue by imposing a time-restricted feeding regimen in which all caloric intakes occur consistently within ≤ 12 h every day. It led to the prevention of excessive weight gain, improvement in sleep and reduction in age and diet-induced deterioration in cardiac performance.

A study⁸ (Melkani & Panda, 2017) in rodents showed that time-restricted feeding reduced metabolic disease risk by maintaining metabolic homeostasis (stabilization).

Limiting food access to daytime 12 hours every day in common fruit flies resulted in prevention of weight gain, improved sleep and deceleration of cardiac ageing. This was a 2015 study⁹ (Gill et al., 2015) that suggested that when even when the caloric intake and activity were unchanged, time-restricted feeding reduced the risk of cardiac ageing.

4. Stabilize Cholesterol

Time-restricted feeding (TRF) has also been shown⁴ (Chaix et al., 2014) to reduce whole-body fat accumulation and associated inflammation. It also induced nutrient homeostasis (stabilization), which in turn, improved and restored metabolic rhythms regardless of the diet and enhanced metabolic capacity. This ultimately resulted in better fitness in mice subjected to TRF.

It has also been observed to reduce whole-body fat accumulation and associated inflammation.

5. Improve Fitness

Time-restricted feeding (TRF) has also been shown⁴ (Chaix et al., 2014) to reduce whole-body fat accumulation and associated inflammation. It also induced nutrient homeostasis (stabilization), which in turn, improved and restored metabolic rhythms regardless of the diet and enhanced metabolic capacity. This ultimately resulted in better fitness in mice subjected to TRF.

It has also been observed to reduce whole-body fat accumulation and associated inflammation.

6. Protect Against Type-2 Diabetes

A study⁴ (Chaix et al., 2014) analysed whether time-restricted feeding could potentially protect against obesity-associated insulin resistance and type II diabetes.

It summarized that time-restricted feeding did improve glucose homeostasis (stabilization) and reduced insulin resistance in animals under the nutrition conditions that represented modern diets. It also reversed previously established glucose intolerance caused by diet-induced obesity.

7. Prevent Fatty Liver Disease

Fatty liver is the most common liver disease in the United States. If not addressed at the right time, it may develop into more serious liver problems or raise the risk of heart-related ailments.

A study⁷ (Chaix et al., 2019) showed that time-restricted feeding may prevent fatty liver in clock mutant mice.

A study⁵ (Megumi et al., 2012) in mice found that additional gene expression signatures often associated with hepatic (liver) inflammation and fatty liver disease were either reversed or reduced under a time-restricted feeding regimen.

The aforementioned are some of the positive results obtained from medical research. As you can see, most of these studies were conducted in mice.

Things to be Careful About Time-Restricted Feeding

• Make Sure It Is Something That Suits You

Just like certain types of food, not everyone may be cut out for a diet of this type. And more than the diet itself, its intensity is of more concern.

The intensity would include the duration of the restricted phase and consecutive days for which you go on the diet. The definition of this “intensity” will vary from individual to individual based on their physiology and needs.

Consulting a doctor before you undergo this and disclosing your targeted restriction period and the number of days you intend to do this can help him/her tie that to your current physical state and provide proper advice.

• This Is Not For Children

It may not be a good idea for children below puberty to undergo this type of diet, especially at a high intensity (14-16 hr. restriction).

While there is no adequate proof for this claim, a study¹⁰ (Hu et al., 2019) in mice did test how time-restricted feeding may affect juvenile mice. The results were that time-restricted feeding in childhood may cause severe irreversible adverse metabolic disorders, depressed immune function, retarded puberty, unhealthy gut micro-biota, fatty liver disease, tendency to gain body weight, higher levels of serum glucose etc. 

While that may have been a study in mice, that list of adverse effects is just too serious (not to mention long) to take a chance on.

• Avoid Dehydration

Please keep in mind that your version of the time-restricted feeding should include consumption of plenty of non-caloric fluids (mainly water) during the restricted period so that you avoid dehydration. It is something that many people miss out on. Inadequate hydration may lead to kidney-related malfunctions.

Clearly, there is a need for more human-based studies regarding this diet. While all the aforementioned studies in mice are highly indicative of the same mechanisms operating in the human body, these are still simulations at best. There is a need for more extensive studies in humans for getting more relevant, concrete results. 

In any case, time-restricted feeding is a much-discussed and promising method that may, in future, be used to treat obesity and lifestyle diseases.