A disturbing link has been identified between weight gain and juice drinking.

“One of the fundamental problems with juice is quantity; It’s very easy to overdose on fruit this way,” says co-author and leading nutrition researcher Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. School of Public Health. T.H. Chan and professor of medicine at Harvard Medical School in Boston.

“For example, how often do we eat three oranges? However, a glass of orange juice is about three oranges that can be eaten in a minute or two, and we can go back and drink more, which will add a lot of calories and cause our blood glucose levels to spike,” notes Dr. Willett.

Over time, too much blood sugar can lead to insulin resistance, metabolic syndrome, diabetes, heart disease, obesity and other chronic conditions, experts say.

Although the study’s findings did not show a direct cause-and-effect relationship, only an association, the results were “very reasonable and consistent with what we see clinically,” said pediatric endocrinologist Dr. Tamara Hannon, a member of the American Academy of Pediatrics (AAP) nutrition committee, who did not take participation in the study.

Due to concerns about rising rates of childhood obesity and dental caries, the AAP advises parents and caregivers to avoid juices entirely for children under 1 year of age, limit intake to 4 ounces per day for children ages 1 up to 3 years old and only 6 ounces per day for children ages 4 to 6 years old, notes CNN.

“There really is no medical reason to drink juices instead of whole fruits and vegetables unless your child is intolerant of regular foods,” said Hannon, director of the pediatric diabetes program at Riley Children’s Hospital and professor of medical and molecular genetics at Indiana University School of Medicine in Indianapolis.

According to national dietary guidelines, teens and adults should drink no more than 8 ounces of 100% juice per day, and juice should not be considered a healthy thirst quencher.

“General recommendations are against ‘routine’ eating—in other words, relying on juice rather than water to quench thirst, or drinking juice specifically for health benefits,” says Dr. David Katz, a preventative and lifestyle medicine specialist. , who founded the nonprofit True Health Initiative, a global coalition of experts. He did not take part in the study, CNN emphasizes.

“It’s not for daily health maintenance—it’s an occasional sweet treat. In this context, fruit juice is a much better choice than soda for many reasons,” notes Dr. Katz.

For some, the concern about 100% fruit juice can be confusing—fruit is healthy, right? So, what is the difference between fruit and fruit juice?

“Whole fruits and vegetables contain a large amount of nutrients – carbohydrates, proteins, fats, minerals and vitamins, which are found along with fiber. This is how our body should receive nutrition, explains Tamara Hannon. “When we remove the casing, we remove the fiber and structural components of the food, and our bodies digest and metabolize it differently than it did during evolution.”

For example, eating a whole apple does not spike your blood sugar because fructose, a sugar naturally found in fruits and some vegetables, enters the blood slowly. However, drinking apple juice saturates the blood with fructose.

“Blood cannot be sweet. This is dangerous for your organs, so the body has many mechanisms to quickly get rid of sugar and keep blood sugar levels normal, Hannon explains. “So the liver, which metabolizes sugars, converts most of those calories into fat, which can be easily stored and not removed from the blood.”

That’s not the only impact, adds study author Vasanthi Malik, a research fellow in the department of nutrition at the Harvard T.H. School of Public Health. T.H. Chana.

“When you consume calories in solid form, your brain is better able to register those calories and adjust your food intake accordingly,” says Malik. “But if you drink those calories, you may not feel full and start eating again.”

The meta-analysis, published Tuesday in JAMA Pediatrics, analyzed 42 studies: 17 in children and 25 in adults.

“The benefit of a meta-analysis is that it requires small studies and brings all the data together so it can be analyzed as if it were one large study,” says Tamara Hannon.

In children, each additional serving of 100% fruit juice per day was associated with a 0.03 increase in body mass index, or BMI, according to the study.

The study initially found no effect on adults due to differences in the way calories are measured, Vasanti Malik points out. However, when only the subset of 25 studies that adjusted for calories were analyzed, the results showed a small change in BMI of 0.02.

To calculate an adult’s BMI, weight is divided by the square of the person’s height. A child’s healthy weight range is based on a BMI between the 5th and 85th percentiles on the CDC growth charts. Because the calculation is more complex, parents and caregivers should never use an adult BMI calculator to determine their child’s weight, the CDC says.

While the changes in BMI found in the study may be small per person, “when you look at a small number across the entire world population, it has a huge impact, especially since most people don’t drink 4 ounces of juice a day, which is a standard serving,” says Hannon.

“They drink 16, 20, 24 ounces of juice a day, which is then associated with a significant increase in BMI,” she said. “My advice to parents is to always discuss this with your doctor, but don’t consider juice a healthy drink when you’re thirsty.”

“Offer whole fruits for snacks and treats if your child can eat them,” adds Hannon. “And if you use juice as a fruit serving, it should be half a glass, no more, per day.”