The research, published on January 23rd in the JAMA Pediatrics journal, revealed a positive correlation between the intake of 100% natural fruit juice and the Body Mass Index (BMI) – a measurement considering weight and height – particularly in children.

Furthermore, a correlation was observed between the daily intake of 100% fruit juice and weight gain in adults.

The term "100% natural fruit juice" was defined as fruit juices without any added sugar.

Although the increments were modest – for instance, in children, each extra daily serving was linked to a BMI increase of 0.03 – the variations were influenced by age, with apparently more significant BMI increases in younger children.

"The analysis suggests that in the case of younger children", those under 11 years old, "they showed a greater increase in BMI for each additional serving of 236.59 ml per day of 100% fruit juice than older children", noted the study authors.

This doesn't mean we should completely give up juices; the study suggests being more mindful of how much 100% natural juice we consume.

"The findings support public health guidelines to limit the consumption of 100% fruit juice to prevent overweight and obesity", the authors wrote.

It also raises the question: If fruits are good and recommended as part of a healthy diet, why can 100% fruit juice lead to weight gain?

The authors point to a possible factor: "liquid calories".

"A potential mechanism linking 100% natural fruit juice to weight gain is the consumption of liquid calories, which has been shown to result in greater weight gain compared to ingesting solid calories", they noted.

Juice contains "few or no fibers compared to whole fruits, leading to low satiety", they added, meaning that juice won't make us feel as full as consuming whole fruits.

The authors also noted that the study's findings are in line with the recommendations of the American Academy of Pediatrics (AAP), stating that children under 6 years old should consume "less than one glass of fruit juice per day", with a typical glass being almost 240 milliliters.

AAP and the Centers for Disease Control and Prevention (CDC) also recommend that for children under 1 year old, juices should be entirely avoided.

AAP's recommendations for other ages are as follows:

Children between 1 and 3 years old – limit juice to a maximum of 120 milliliters (ml) per day. Children between 4 and 6 years old – limit consumption to 170 ml. Children between 7 and 18 years old – limit to 240 ml per day.

To enjoy a fruity flavor with fewer calories, the CDC recommends adding a splash of 100% juice to flat or sparkling water for a "refreshing, low-calorie beverage".