My client Caroline, who had been losing weight successfully for a month, was disappointed one recent week when she failed to do so. It didn't make sense. Her food intake was stellar, and she had been even a little more physically active than usual. It wasn't until we reviewed her food diary thoroughly that we discovered the culprit: liquid calories. They added up in a way that surprised her.
As for many of us over the holidays, that extra glass of wine or mixer here and there adds up in ways that you might not expect. Though liquid calories in alcohol, juices or sodas are stealthy, their impact can be enormous.
When food is consumed before or during a meal, the volume and caloric content of that food will limit what else you eat fairly proportionately. Most caloric drinks consumed before or during a meal are not satiating and have little or no effect on how much you eat in one sitting or over the course of several meals.
Scientific evidence is confirming that our bodies don't detect the calories in these liquids the same way as when we eat solid foods.
"Fluid calories do not hold strong satiety properties, don't suppress hunger and don't elicit compensatory dietary responses," says Richard D. Mattes, professor of food and nutrition at Purdue University. In fact, "when drinking fluid calories, people often end up eating more calories overall."
It's fairly well established that alcoholic beverages and sugary liquids, especially sodas and fruit drinks, simply add more calories.
This may help explain the results of the recent Harvard Nurses' Health Study of more than 50,000 women over eight years. Researchers found that those who increased their intake of sugar-sweetened beverages, such as sodas or fruit punch, from one per week to one or more per day consumed an average of 358 extra calories per day and gained a significant amount of weight. The women who reduced their intake cut their calories by an average of 319 and gained less weight.
Studies in previous years demonstrated that consumption of sugar-sweetened soft drinks increased the likelihood of obesity in children, but this is the first finding from a long-term observational study in adults.
The mechanisms controlling hunger and thirst are completely different: Although liquids may contain calories, they don't seem to satisfy hunger even if they quench your thirst. Physiologically, your thirst is quenched once your blood and cell volume are increased by water. This sends signals to your brain that you are no longer thirsty.
In contrast, hunger is regulated in your stomach and intestines. While you're eating, nerves in the stomach wall detect that the stomach is stretching and send satiety signals to the brain. The intestines also release nerve regulators and hormones. At the same time, the level of the hunger hormone (called ghrelin), which is released by the stomach when it's empty, is suppressed. All this helps you feel full.
Because liquids travel more quickly than food through the intestinal tract, they alter the rate of nutrient absorption, which can affect satiety hormones and signals.
Several theories may help explain why liquid calories cause lower satiety, increasing overall calorie intake, but the process is still not fully understood. The mouth feel of a liquid versus solid food may generate different signals; it takes less time and involvement to gulp down a drink, and that might reduce the psychological satisfaction of eating.
New research has found that ghrelin doesn't work as well with liquids: "When the number and type of calories are the same, the calories in liquid form won't suppress ghrelin as effectively as if the same calories were in solid form," says David E. Cummings, associate professor of medicine at the University of Washington and the Veterans Affairs Puget Sound Health Care System.
A study that will be published soon in the journal Appetite tested the effect of drinking water, diet cola, regular cola, 1 percent milk and pulpy orange juice during meals. It found that drinking water or diet cola had no effect on the total caloric intake of the meal. But with the caloric beverages, each of which contained 150 calories, the subjects consumed 105 more calories overall at each meal.
"People need to be mindful of the calories in beverages," says Barbara J. Rolls, who conducted the study and is co-author of "The Volumetrics Weight-Control Plan" (HarperTorch, 2003). "Most people think calories in beverages don't count and that's how they get into trouble."
When you consider that an appropriately sized meal is anywhere from 400 to 700 calories, and one 44-ounce Super Big Gulp is 800 calories, you understand the scope of the problem. A 16-ounce Starbucks blended coffee Frappuccino is 470 calories. A single mixed drink can set you back 300 calories or more. One glass of wine contains at least 100 calories. Double or triple these numbers at any given party, tack on the calories in your meals, and you can understand how weight gain is the inevitable.
My clients who have become aware of liquid calories have achieved impressive results. Take Bob Levey, former Washington Post columnist, who wrote about the importance of cutting out his daily lemonade in his successful weight loss effort. Another client, Julie, easily switched from her daily Frappuccino to a cafe skim latte (coffee with steamed nonfat milk) and saved 250 calories. My friend Linda slowly phased out her daily soda ounces by filling her glass with increasing amounts of ice each week. She lost 30 pounds over a year.
Since liquid calories don't contribute to feelings of satiety, cutting back on them doesn't make people feel deprived; most find the change is an easy one to make. There are so many great substitutes. The one liquid that's important to keep drinking is water. In the wintertime, I love sipping (mostly water) herbal teas through the day. In the summer, it's seltzer with a twist of lemon or lime, and the occasional diet soda.
Of course, if we are mindful of our calorie intake, a moderate daily dose of wine or other caloric beverage can easily be integrated into our routines. Moderation is the key.
Katherine Tallmadge is a Washington nutritionist and author of "Diet Simple" (Lifeline Press, 2004). Send e-mails to her at firstname.lastname@example.org.