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Adding fresh fruit to your diet is one way to help prevent midlife weight gain. Catherine Falls Commercial/Getty Images
  • Researchers report that eating more refined carbohydrates can lead to more weight gain in midlife.
  • They suggest replacing refined carbs with carbohydrates from whole grains, fruit, and non-starchy vegetables.
  • They added that the link between carbohydrates and weight gain was more significant in women and people with excess weight.

Increased carbohydrate consumption from refined grains, starchy vegetables, and sugary drinks is associated with more significant weight gain throughout midlife, according to a study published on September 27 in the journal BMJ.

Researchers used data on 136,432 men and women, 65 and younger, who enrolled in the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study.

At enrollment, participants were free of health conditions such as:

The participants completed questionnaires on personal characteristics, medical history, lifestyle factors, and other health information at the start and every two to four years until the end of the study (24 to 28 years).

On average, participants gained 3 pounds every four years and nearly 19 pounds over the length of the study.

Researchers reported that weight gain was associated with increases in the glycemic index and glycemic load, which are measures of the effects of different foods on blood sugar levels.

“This is a well-designed study that shows us a relationship but not a causation between types of food we eat and weight gain in midlife,” Dr. Holly Lofton, a physician at NYU Langone in New York specializing in obesity medicine who was not involved in the study, told Medical News Today.

Experts noted the study’s limitations include the fact it was observational and cannot specifically determine the cause. They added it also relied on self-reported data.

The study did home in on some factors that experts consider important.

“This study reaffirms what we know about simple sugars contributing to weight gain, said Dr. Mir Ali, a bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in California, who was not involved in the study. “And although we did know, it wasn’t previously well documented.”

He noted that the associations were stronger among women and those with excessive body weight.

“For women, this could be true because of hormones and how they affect the metabolic process,” Ali told MNT.

The cause might be different for people with excess weight.

“Folks who are already at a higher body weight have higher calorie needs,” Caroline Thomason, a Washington D.C.-based registered dietitian who was not involved in the study, told MNT. “Thus, they might be more likely to over-consume these foods without realizing how much they eat.”

The researchers noted that the study highlights the importance of carbohydrate quality and long-term weight management, especially for people with excessive body weight.

“I explain it to my patients this way,” Ali said. “Think of carbs as a fuel source. If you take that away, your body is forced to burn fat.”

Nutrition experts use five good groups as a basis for their guide to daily eating.

The current study found the types of foods that resulted in weight gain were those with starches and added sugars.

Over four years, the participants who increased their consumption of starch or added sugar by 100 grams per day increased their weight by approximately 3 pounds and 2 pounds, respectively. Meanwhile, raising fiber content by 10 grams per day led to roughly 1.7 pounds less weight gain over four years.

“Weight gain happens when we eat more calories than we burn, said Thomason. “Calories from refined carbs and sugars are much easier to over-consume in total portions and calories. Thus, it makes sense that folks who eat more of these foods tend to increase in weight.”

The researchers reported that replacing carbohydrates from refined grains, starchy vegetables, and sugar-sweetened drinks with equal servings of carbohydrates from whole grains, fruit, and non-starchy vegetables was associated with less weight gain.

“Not all calories are created equal and I agree that carbohydrate quality often plays a bigger role in weight loss or gain than quantity (total grams per meal or day),” said Anne Danahy, a registered dietitian nutritionist specializing in healthy aging, menopause, and chronic disease prevention and management who was not involved in the study.

“Refined carbs and high glycemic foods are metabolized far differently than higher fiber, low-glycemic foods,” Danahy told MNT.

“As you approach middle age, most people, especially women, develop some degree of insulin resistance, which promotes fat storage and makes it harder to lose weight,” Danahy said. “Even if you’re not eating excess calories, a diet high in refined carbs and added sugar can worsen insulin resistance and promote weight gain.”

“I encourage people to count fiber instead of carbohydrate grams. Aim for at least 25 and, ideally, 35 grams of fiber daily. High-fiber foods take longer to digest, keeping you full longer, so you’ll automatically eat less. Fiber also helps balance your glucose and insulin levels. In my years of working with clients, so many people are pleasantly surprised at how much easier it is to lose weight and maintain it once they pay more attention to the quality of their diet instead of how many calories or carbohydrate grams they eat.”

— Anne Danahy, registered dietitian nutritionist

People who are already overweight are likely to be vulnerable to unhealthy diets due to a combination of genetic and social factors, so increases in unhealthy foods are likely to affect them more severely, explained Walter Willett, a professor of epidemiology and nutrition at the Harvard T. H. Chan School of Public Health in Massachusetts and one of the study’s authors.

“Health professionals should be incorporating nutritional evaluation and counseling more regularly than presently,” Willett told MNT.

“As part of this, medical professionals can emphasize the importance of including whole grains and non-starchy vegetables in diets instead of refined grains, sugary beverages, and starchy vegetables like potatoes,” he added.