Diet Drinks Help Weight Loss

The meme that drinking
diet sodas causes weight gain has been ricocheting around the
Internet for years. Generally, this claim has been based on
observational studies in which researchers find that fat people
tend to drink more diet drinks than do skinny people. This has
always seemed to me to be a case of post hoc
ergo propter hoc, i.e., after this, therefore because of
this.

I know that I will annoy some epidemiologists, but a large
proportion of observational studies seem only slilghtly
more respectable than casting horoscopes. Why? Because, even
with the best will in the world, it’s nearly impossible to
eliminate confounders so that a real causal relationship might be
revealed.

A new
randomized trial study in the journal Obesity (and
funded by beverage companies) followed more than 300 people through
a weight loss program. The only difference is that half were asked
to drink at least 24 ounces of water per day and other half to
drink 24 ounces of non-nutritive sweetened (NNS) beverages per
day.

The program involves 12 weeks of losing weight followed by 9
months of weight maintenance. The study found that those consuming
diet drinks lost an average of 14.2 pounds whereas those drinking
water dropped an average of 10 pounds. The researchers chose 12
weeks as the length of the study because prior work shows that
weight loss slows considerably after six months in a treatment
program. (I know from personal experience that that is so.)

The study further notes:

Based on the design of this study we are unable to say, what is
the mechanism for the greater weight loss in the NNS group compared
to the water group. Weekly hunger scores were significantly lower
among the NNS group than the water group although the absolute
changes were small. While it is plausible that the NNS participants
were more likely to adhere to the dietary recommendations due to
less hunger than the Water group we cannot conclude this based on
this study. Some authors have suggested that use of NNS may
increase appetite for sweet foods and disrupt regulation of energy
balance. Weight loss results for the present study suggest that NNS
consumption did not increase energy intake from other foods
compared to water. This is consistent with other studies that have
not found increased consumption of sweet or high energy foods while
using NNS. Further studies will be needed to ascertain the
mechanism(s) that may be responsible for the weight loss
results.

Look, it may turn out that the observational studies suggesting
that drinking diet sodas make people fat are true, but I wouldn’t
bet on it. It has always seemed much more plausible that obese
people drink diet soda because they don’t want to get even fatter
by consuming the extra calories in sugar-sweetened drinks.
Sometimes interestingly counterintuitive claims are bunk. So diet
soda drinkers unite! You’ve nothing to lose but your excess
avoirdupois!