As it turns out -- they might have a secret weapon.
The water bottle is a workout staple, and certainly a good drink for those who are trying to maintain a slender figure.
But according to new research, women may gain less weight over time if they turn that water into wine.
"Women who consume light to moderate amount of alcohol actually experienced a smaller weight gain," said Dr. Lu Wang with Brigham and Women's Hospital.
Wang followed nearly 20,000 healthy, middle-aged and older women.
Some weight gain was typical over the 13-year study period.
But women who started with a normal weight were less likely to gain extra pounds if they drank light to moderate amounts of alcohol.
That means no more than 2-3 servings of beer or wine each day. The link was strongest for red wine.
While it's true these women had healthy lifestyles overall, there seems to be something about the alcohol itself. Women who didn't drink any gained the most weight.
And rather than break bread with their wine, moderate drinkers also tended to eat smaller portions, cutting out carbs in particular.
The bottom line? For healthy women who already have a glass or two with dinner: "They could keep their drinking habit without gaining more weight," Wang said.
And if exercise is also a habit, a little tipple could help tip the scales in your favor.
Researchers also found an association with white wine and less weight gain -- but the link was strongest with red wine.