Study shows liquid calories trick body and mind to overeat

A calorie’s a calorie, isn't it?  Well, accumulating evidence shows that our body has a hard time registering calories from beverages in the tally towards satiety; unfortunately, these beverage's calories still count in our energy balance.  That’s why the extra calories in beverages are just extra—much like items that didn’t go into the budget, but will nevertheless have to be paid for.

There are numerous studies to prove this point; here are just a few:

Nutritionist Barbara Rolls from Penn State served women water, diet soda, regular soda, orange juice, milk or no drink with 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.

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

A study by Richard Mattes and Wayne Campbell of Perdue University looked at the effects of food form (solid, semi-solid or liquid) on appetite.  Participants consumed either a whole apple, applesauce or apple juice of equivalent caloric value. The apple juice reduced hunger the least, the whole apple reduced hunger the most and the applesauce response was intermediate.  The participants that had the beverage apple where ready for their next meal almost an hour earlier than those that had a bitable apple.

Is satiety in our senses or in our heads?

Previous research suggests that a fluid consistency leads to less satiety.  Beverages require less chewing, and travel faster through the stomach and the intestine, explaining the lower satiety effect.

But we also eat and get full in our mind.  Could it be that it’s our mind that doesn’t see fluids as food, and therefore fails to register beverage’s calories?

To try and tease apart the physiological from the psychological a new study led by Bridget Cassady and published ahead of print in the American Journal of Clinical Nutrition devised an interesting experiment.  Fifty-two healthy adults were treated to a pre-lunch “appetizer”, consisting of 10 percent of their daily caloric needs.  Each participant experienced 4 different pre-lunch settings, all containing exactly the same amount of calories:

• Liquid to liquid: participants consumed a clear, cherry flavored drink.  Study administrators demonstrated what happens in the body by mixing the drink with what they called “gastric acid”, but was really ordinary tap water.  The mix didn’t change the liquidity of the pre-meal, therefore participants drank a liquid, and believed it remained liquid in their stomach.

• Liquid to solid: participants consumed the same clear, cherry flavored drink.  Study administrators demonstrated what happens in the body by mixing the drink with what they called “gastric acid”, but this time it was calcium chloride, which formed a solid mass upon mixing, therefore participants drank a liquid, but believed it turned solid in their stomach.

• Solid to liquid: Participants consumed cherry flavored gelatin cubes.  The study administrator imitated what happens in the stomach by mixing the gelatin cubes with “gastric acid” which in this setting was warm water, which melted the cubes, leading participants to believe that although they swallowed a solid, their stomach experienced a liquid.

• Solid to solid: Participants consumed cherry flavored gelatin cubes.  The study administrator imitated what happens in the stomach by mixing the gelatin cubes with “gastric acid” which in this setting was cold water, which didn’t affect the cubes’ solidity, leading participants to believe that they swallowed a solid, and their stomach is digesting a solid.

Hunger, fullness and appetite were assessed after each pre-meal, as well as objective measures such as blood glucose, insulin and ghrelin, stomach emptying and intestinal transit time and caloric intake in the meal following the test pre-meals.

And the results:

Liquid meals and perceived liquid meals were followed by greater hunger and less fullness.  Participants’ responses to liquid to liquid and solid to liquid pre-meals included: ”this didn’t fill me up at all” and “it hardly feels I ate anything”.  On the other hand, the solid meal (solid to solid) and perceived solid meal (liquid to solid) elicited responses such as “ I can’t remember ever being so full” and “it feels like I swallowed a rock”.

Participants ate more (in the post-test meal) when they thought they’re eating liquids – 22 percent more, which amounted to about 160 additional calories.

Stomach emptying and transit time in the colon were faster when taking in liquid or when believing the solid turned into liquid.

Insulin and other hormones signaling satiety had an attenuated rise when consuming liquids. Ghrelin, a hormone, which is suppressed after meals, was less suppressed by the liquid pre-meals.

Thinking about liquids is enough to diminish satiety

This study confirms that liquid calories cause less satiety, and also shows that just thinking about food in liquid form increases not only hunger levels but also measurable physiologic responses such as the rate in which the stomach empties and the levels of hormones that affect appetite.

Why does our body seem oblivious to the calories in drinks? Perhaps it can be explained by looking at human history: Throughout most of human times 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, available for purchase practically everywhere. These liquids calories don't seem to satisfy hunger and are therefore a source for calories that just sneak up on us.

Dr. Ayala

Full disclosure: I’m vice president of product development for Herbal Water, where we make organic herb-infused waters that have zero calories and no sugar or artificial ingredients. I’m also a pediatrician and have been promoting good nutrition and healthy lifestyle for many years.

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