Why do liquid calories in sugary drinks matter so much?

Many experts see sugary drinks as a major contributor to overweight and obesity. Large, well-preformed studies such as Harvard’s Nurses' Health Study, which followed more than 50,000 women, have shown a correlation between consumption of sugary drinks and expanding waistlines.

Is this just a correlation, or is there a clear cause-and-effect relationship between the two? Is there something special about sweet beverages that sets them apart from other low-nutritional-value foods, and justifies “blaming” them for a disproportionate contribution to the obesity epidemic?

The science community generally agrees that when it comes to weight control a calorie is a calorie is a calorie, and weight gain is a result of consuming more calories than what one spends no matter where the calories came from. Calories from fats or carbs, junk food or gourmet meals all add up in the same way, and weight gain is just a matter of energy imbalance, in which the extra energy accumulates as fat.

On the other hand, research shows that some eating patterns are more conducive to overeating and overconsumption. Paramount among the foods that lead to an overconsumption pattern are sugary drinks.

There’s mounting evidence showing that when we drink beverages with calories we don’t compensate by eating less food, and the extra calories in beverages are, well, just extra—much like items that didn’t go into the budget, but will nevertheless have to be paid for.

There are many studies to prove this point; here’re just a few:

Nutritionist Barbara Rolls from Penn State gave women water, diet soda, regular soda, orange juice, milk or no drink before lunch. Those given caloric beverages consumed about 100 calories more than those given diet soda, water or no beverage at the meal, without significantly affecting satiety ratings (see here).

In the cute Jelly bean study, researchers gave men and women 450 calories a day of either soda or jelly beans for a month, then switched them for the next month and kept track of total consumption. Candy eaters ate less food to compensate for the extra calories. Soda drinkers did not, so they ate more calories than usual.

A new study by Richard D. Mattes and Wayne W. Campbell of Perdue University in the current edition of the Journal of the American Dietetic Association looks at the effects of food form (solid, semi-solid or liquid) on appetite and adds to this body of evidence.

In this study the researchers had twenty lean and twenty overweight men and women consume either a whole apple, apple sauce or apple juice of equivalent caloric value. The experiment was preformed with each participant six times, giving each person a chance to eat each of the apple forms twice, once as part of a provided fixed portion meal and once two hours after a meal.

The intent of the study was not revealed to the participants. They were actually told that what’s being tested is the food’s effect on their motor skills (which were also tested).

Appetite assessment was assessed by questionnaires, and diet records were kept for the duration of the experiment.

Here are the main results:

• The apple juice reduced hunger the least, the whole apple reduced hunger the most and the applesauce response was intermediate whether consumed with a meal, or alone as a snack.

• The appetite suppression was greatest for the whole apple when consumed as a snack.

• The participants could eat freely once they left the lab. Those that had the beverage form where looking again for food almost an hour earlier than those that had a whole apple, whether they had the food in a meal or as a snack (although in this study the subjects didn’t report they ate more after the liquid apple).

• There were so significant differences between the lean and the obese participants in regard to appetite suppression.

The authors conclude:

“Our findings suggest beverages consumed alone as an afternoon snack or when incorporated into a midday meal lead to comparable, weak appetitive effects. Stronger effects were noted with a solid form of the same food and intermediate effects were observed with a semisolid form. This suggests that energy-yielding beverage consumption poses a particular risk for promoting positive energy balance when consumed either as a snack or with a meal.”

Throughout most of human history people ate food when they were hungry, and drank water when they were thirsty. Beverages with calories were rare. Nowadays, sugary beverages constitute about a fifth of the daily caloric intake and are probably the most ubiquitous food item, ready for purchase practically everywhere. These liquids calories don't seem to satisfy hunger (even if they do quench thirst) and are therefore a source for calories that just sneak up on you.

Looking at these studies I’d say that eating solid candy is probably a better strategy to controlling appetite than consuming that candy in liquid form, which I daresay is pretty much what many sugary drinks really are.

The good news is that since liquid calories don't make you any less hungry cutting back on them is usually quite easy, and probably the most rewarding first step to make towards a healthier diet and a healthy weight.

Dr. Ayala