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A new study finds that intermittent fasting may help people with type 2 diabetes lose weight. Caíque de Abreu/Getty Images
  • Maintaining a healthy weight is critical for helping those with diabetes manage blood sugar levels.
  • New research indicates that time-restricted eating is more effective for weight loss than counting calories.
  • Simplicity and impacts on hormones are two reasons why fasting may aid weight loss.
  • However, those with diabetes should be mindful of time-restricted eating, especially if taking medication.

Around 37 million Americans or 1 in 10 are diagnosed with diabetes, with the majority having type 2 diabetes. Of these individuals, up to 90% have overweight or obesity.

New study findings, shared this week at NUTRITION 2023, the flagship meeting of the American Society for Nutrition, indicate that traditional calorie restriction is not the most effective way for people with type 2 diabetes to shed extra pounds.

Instead, they suggest that time-restricted eating also called intermittent fasting — only consuming food in an eight-hour window — is a more beneficial approach for those looking to lose weight.

While the study is currently under peer review and awaiting journal publication, the results highlight further opportunities for people with type 2 diabetes looking to reduce their weight and improve blood glucose levels.

Studies have previously explored the efficacy of different dieting approaches among those with obesity. However, none have investigated the potential impact of time-restricted eating in people have who obesity and type 2 diabetes.

The new research, led by Vicky Pavlou, RDN, a doctoral student at the University of Illinois at Chicago, involved 75 obese adults with obesity, who had type 2 diabetes. Participants aged between 18 and 80 years old were split into three groups: control, calorie restriction, or time-restricted eating.

Those in the control group continued eating as usual, and those undertaking calorie restriction reduced their maintenance calorie intake (the amount required to maintain their current weight) by 25%. They could eat at any time of the day.

Meanwhile, the time-restricted eating group was not given an assigned calorie goal and did not track their calorie intake — but could only eat between noon and 8 pm each day.

For support, participants from both groups met with a dietitian once a week for the first three months of the study and every other week for the remaining three months.

“The dietitian helped them with any challenges in following the diet and gave general nutrition advice,” Pavlou explained to Healthline — including “the importance of reading labels and understanding calories.”

The participants followed the diets for six months. After this time, the calorie restriction group did not experience any weight loss relative to the control group. On the other hand, relative to the control group, the time-restricted eating group lost an average of 3.55% body weight.

“I was surprised that the [calorie restriction] group did not lose more weight,” Pavlou said. “In most studies, the [time-restricted eating] and calorie restriction groups lose the same amount of weight.”

In addition, both the time-restricted eating and calorie-restriction groups demonstrated a decrease in average blood glucose levels as measured by HbA1c compared to those in the control group.

The findings are important, stated Pavlou, as they offer another potential weight loss strategy for those with type 2 diabetes.

“Some people find it difficult to count calories,” she said. “Others don’t have weekly or monthly support and need a dietary pattern that is simple to follow, such as watching the clock.”

There are a couple of reasons why intermittent fasting or time-restricted eating may have been more effective in encouraging weight loss.

After analyzing the data, it was noted that “the [time-restricted eating] group was more adherent to their diet than the [calorie restriction] group,” Pavlou explained.

But why might this have been? “Most participants in the [time-restricted eating] group reported that the diet was easy to follow,” she said. Meanwhile, “at least half the participants in the [calorie restriction] group reported the diet was difficult to follow.”

Another primary factor is the difference in calorie reduction between the two groups. Even though researchers told the time-restricted eating group not to cut or track their calorie intake, they “reduced their intake by 313 kcal per day,” revealed Pavlou.

Yet, despite actively working to reduce calories, the calorie restriction group only saw their average intake lower by an average of 197 kcal daily.

“The [time-restricted eating] group had only 8 hours to eat their calories, so they naturally reduced their intake (no breakfast or post-dinner snacking/drinking),” said Pavlou. “I thought the [calorie restriction] group would do better, but I think they did not track very accurately or consistently enough.”

Kelsey Costa, MS, a registered dietitian and health research specialist at the National Coalition on Healthcare (NCHC), who was not involved with the study, agreed that tracking calories can be difficult for some.

“Traditional methods of calorie counting and tracking food intake can be time-consuming,” she shared with Healthline.

“Even with the assistance of calorie tracking apps, meticulously planning and monitoring daily meals can feel overwhelming, especially for individuals leading busy lifestyles.”

Time-restricted eating is a type of intermittent fasting in which meals are consumed in a smaller window of time — usually between 4 and 12 hours.

By creating alternating phases of feeding and fasting, “the underlying idea is that this pattern can positively affect nutrient metabolism, hormonal regulation, and physiological processes, ultimately enhancing cardiometabolic health,” said Costa.

During “fasting” periods, your body relies on its fat stores for energy. “This metabolic process promotes weight loss by utilizing internal resources,” Costa explained to Healthline.

But time-restricted eating is thought to encourage weight loss through other means, too — such as reducing opportunities to snack.

This fasting approach “may also help regulate hormones associated with hunger and satiety, leading to decreased caloric intake,” said Costa.

Furthermore, she added, “Research suggests that time-restricted eating can help improve insulin sensitivity and decrease inflammation, which can improve glycemic control and weight loss.”

Although intermittent fasting or time-restricted eating is believed to have benefits, there are also risks and side effects to be aware of — particularly for those with diabetes.

For starters, “incorrect implementation or lack of guidance can result in nutrient deficiencies, electrolyte imbalances, and dehydration,” explained Costa.

Another key consideration is the impact of time-restricted eating on medications being taken to help control diabetes.

“Certain diabetic drugs require food for absorption and won’t absorb if one is fasting,” said Dr. Pouya Shafipour, a board-certified family and obesity medicine physician at Providence Saint John’s Health Center.

Furthermore, “certain diabetic drugs lower the blood sugar rapidly,” Shafipour told Healthline. “Fasting will put one at risk of low blood sugar levels (hypoglycemia), which can be life-threatening.”

If a patient with diabetes starts undertaking time-restricted eating, it’s recommended that they work with a physician to closely monitor their blood sugar levels, said Dr. Revital Gorodeski Baskin, Assistant Professor of Medicine at Case Western Reserve University and Obesity Program Director at The Diabetes and Metabolic Center, University Hospitals.

She explained that medications can then be quickly adjusted (if necessary) to counter any hypoglycemic effects.

It’s also crucial to note that engaging in time-restricted eating doesn’t mean you can eat all the sweet treats and fries you might like.

“The quality of the food choices matters when it comes to [time-restricted eating,]” stated Costa. “Eating unhealthy processed foods and high-calorie snacks will likely counter any weight loss benefits associated with this diet approach.”

When adopting a new dieting tactic, checking in with your physician before doing so is essential.

Costa shared that numerous factors can make it more challenging for people with type 2 diabetes to lose weight, such as the body’s insulin response, mental health challenges often associated with diabetes (such as depression), and medications.

Yet maintaining a modest weight is crucial for those with this metabolic disorder, as doing so assists in managing blood sugar and reduces the risk of health-related complications.

The good news is you don’t have to drop multiple clothing sizes to experience health benefits.

“With even small percentages of weight loss, insulin resistance improves, as does the diabetes,” said Gorodeski Baskin.

The new study supports the role of time-restricted eating or intermittent fasting in weight loss — although Gorodeski Baskin believes calorie restriction still has a part to play.

“I recommend a consistent [calorie restriction] to most patients, and often encourage [time-restricted eating] as well,” she said. “I think the combination of the two measures helps improve diabetes.”

What you eat is also as important as the amount you eat.

“Consuming a significantly lower amount of simple starches, sugar, and preservatives” can aid weight loss in diabetics, said Shafipour.

Instead, he continued, aim to eat a “lower carbohydrate Mediterranean diet, high in plant-based fat, legumes, fiber, colorful vegetables and seasonal whole fruits, and fish.”

But monitoring food intake (or the clock) isn’t the only approach that can aid in shedding the pounds.

Gorodeski Baskin noted that “Strength training exercises help boost the metabolic rate, and therefore often helps with the weight loss journey.”

Plus, not eating three hours before bed, engaging in daily exercise, and optimizing sleep are all ways to encourage weight loss and improve diabetes, said Shafipour.

New study findings indicate that traditional calorie restriction is not the most effective way for people with type 2 diabetes to shed extra pounds. Instead, experts suggest that time-restricted eating also called intermittent fasting — only consuming food in an eight-hour window — is a more beneficial approach for those looking to lose weight.