For years, people have swapped creamy whole milk for a watery bottle of trim to help boost their weight loss efforts.
But new research has discovered that drinking skinny versions could be making people bigger, not smaller.
Government guidelines currently recommend that people consume "moderate amounts of milk and dairy, choosing reduced fat versions or eating smaller amounts of full fat versions or eating them less often."
It is generally thought that by drinking trim milk you can get whole milk's benefits - Vitamin D, calcium and protein amongst others - without the fat and calories.
By reducing the fat, the trim milk is certainly lower in calories, but the authors of a new study - David Ludwig, of Boston's Children Hospital, and Dr Walter Willett, of the Harvard School of Public Health - believe lower calorie beverages do not necessarily mean lower calorie intake.
They say there is very little data to back up the idea that skimmed milk promotes weight loss or management and that because reduced fat foods might not be as filling, they could lead consumers to compensate by eating and drinking more.
A previous study actually found that those who drank low fat milk had a higher chance of being overweight later on in life, according to Time Magazine.
"Our original hypothesis was that children who drank high fat milk, either whole milk or two per cent, would be heavier because they were consuming more saturated fat calories," said author of the study Dr. Mark Daniel DeBoer, an associate professor of pediatric endocrinology at the University of Virgina School of Medicine.
"We were really surprised when we looked at the data and it was very clear that within every ethnicity and every socioeconomic strata, that it was actually the opposite, that children who drank skim milk and one-percent were heavier than those who drank two-percent and whole."
It should be noted that even full-fat milk only contains three to four per cent fat anyway.
In addition to this, companies trying to sell reduced-fat milk products may also increase sugar levels to make them taste better.
One glass of low-fat chocolate milk contains 158 calories - 68 of them coming from solid fats and added sugars - while a glass of unflavoured, semi-skimmed milk has 122 calories, with 37 of them coming from solid fats and sugars.
"Somehow this low-fat milk has become so entrenched in the nutritional psyche, it persists despite the absence of evidence," said Mr Ludwig.
"To the contrary, the evidence that now exists suggests an adverse effect of reduced-fat milk."
Finally, it should not be forgotten that research has shown that trim milk also provides less nutrients than whole.
Full-fat dairy is a vital source of the fat-soluble vitamins A, D, E and K as well as calcium and phosphorus, the minerals that work with vitamin D for build strong bones.
But the term "fat-soluble" means that these vitamins need to be delivered in or with fat for the nutrients to be available to the body. Taking the fat out makes it difficult or even impossible to absorb them.
The new study was published in JAMA Pediatrics.
- DAILY MAIL