How does it affect blood sugar control?

• Time-restricted eating involves eating all your meals and snacks within a window of 8-12 hours, and consuming no calories outside that window.
• It may have benefits including boosting metabolism, encouraging weight loss, and decreasing the risk of some health conditions.
• Now, a small study has shown that restricting eating to an 8-hour window at any time of day could help people control their blood glucose levels, decreasing their risk of type 2 diabetes.

Time-restricted eating (TRE), one of whose most popular iterations is intermittent fasting, is becoming increasingly popular as a means of weight control.

The most popular form involves eating only during a period of 8 to 12 hours each day, and fasting outside that time, consuming only water and other calorie-free drinks.

Previous studies have suggested that TRE could have several health benefits, which may include:

• weight loss, particularly in those with overweight or obesity.
• improving cholesterol and triglyceride levels in the blood, potentially decreasing the risk of cardiovascular disease
• improving cognitive function
• improving sleep quality
• anti-aging and anti-cancer effects
• improving insulin sensitivity.

The study, which has not yet been published in a peer-reviewed journal, was carried out by researchers at Manchester Metropolitan and Newcastle Universities in the United Kingdom.

Jagdish Khubchandani, PhD, professor of public health at New Mexico State University, who was not involved in this study, told Medical News Today that:

“On the surface, the findings look interesting and in line with other studies. One possible mechanism of action could be that TRE could result in lesser fluctuations in blood sugar, and nutrient shortage over some hours could increase insulin sensitivity. Some recent reviews align with these findings.”

The researchers recruited 15 people into their randomized crossover trial. The nine women and six men had a mean body mass index (BMI) of 28, which is indicative of overweight, a sedentary lifestyle, poor dietary habits, and a mean age 52 years, so were at high risk of developing type 2 diabetes.

The participants alternated between 3 days of habitual eating with an eating window of at least 14 hours per day, 3 days of early TRE where they ate only between 08.00 a.m. and 4.00 p.m., and 3 days of late TRE, where they ate between noon and 08.00 p.m. During TRE, they fasted for 16 hours each day.

The researchers designed eucaloric diets — matching energy intake to energy expenditure — for the participants during the TRE phases, and they were allowed to eat normally during the habitual eating days. These eucaloric diets were made up of 50% carbohydrate, 30% fat and 20% protein.

All participants wore continuous glucose monitors which assessed how much time was spent each day with a normal blood glucose concentration — between 3.9 and 7.8 millimoles per liter (mmol/l).

By comparison with habitual eating, both early and late TRE increased the time that people’s blood glucose was within the normal range by, on average, 3.3%. It also reduced markers of glycemic variability.

“Our study found that restricting eating to a window of 8 hours per day significantly improved the daily time spent in the normal blood glucose range and reduced fluctuations in blood glucose levels. However, altering the 8-hour restricted eating period to earlier or later in the day did not appear to offer additional benefits.”

While acknowledging that these were encouraging findings, Khubchandani expressed some concerns about the study, telling MNT that “it is unclear how such a small sample can cover the heterogeneity among people at risk of diabetes worldwide.”

He also questioned whether the study’s effects were actually due to TRE, wondering: “Does TRE also at times equate to reduced consumption of calories?”

Type 2 diabetes is strongly associated with overweight and obesity. According to Diabetes UK, overweight and obesity account for up to 85% of the risk of developing type 2 diabetes, and people with obesity are up to 80 times more likely to develop type 2 diabetes than those with a BMI of 22 or under.

So, if a person with overweight or obesity finds that TRE is an effective way to lose weight it may help to reduce their risk of developing type 2 diabetes.

However, Khubchandani cautioned that some larger studies have not shown the same benefits as this small study.

Bowden Davies acknowledged that this was a preliminary study, and that further studies were needed to determine whether TRE might be effective for some people, saying that:

“Many people find counting calories hard to stick to in the long term, but our study suggests that watching the clock may offer a simple way to improve blood sugar control in people at risk of type 2 diabetes, irrespective of when they have their 8-hour eating window, which warrants investigation in larger studies and over the longer term.”

As well as the potential benefits shown in this study, there may be downsides to TRE for some people.

One preliminary study of more than 20,000 adults, conducted by the American Heart Association, found that those following an 8-hour TRE schedule had a 91% higher risk of death from cardiovascular disease, and no increase in longevity, compared with those following a standard 12-16 hour eating schedule.

The authors of this study suggest that TRE may have short-term benefits, but could have adverse effects over the long term.

People who are older, pregnant, breastfeeding, trying to conceive, have low blood pressure, or are taking medications for blood pressure or heart disease, should also consult a healthcare professional before they consider intermittent fasting.

“Given the uncertainty, individuals at risk of diabetes should consult a qualified doctor. For the general public, get blood sugar checked regularly. One size doesn’t fit all and diabetes prevention should be more personalized.”

– Jagdish Khubchandani, PhD