I didn't realize how a simple topic like water could spark off so many discussions and questions. A number of readers emailed me about last week's column on the "8 x 8 rule" or the latest scientific finding that the average sedentary person does not need to drink eight glasses of water a day. Some of the questions were about the role of water as a weight loss aid like, "Is it true that drinking a glass of water before eating will make you full?" "They say that drinking water if you are hungry in between meals will keep you from snacking. Is this true?"
The right person to answer those questions is Dr. Barbara Rolls, a research scientist at Penn State University whose field of expertise is the "science of satiety" or the science of what makes people feel full at the end of a meal.
For twenty years, Rolls has been studying the factors that affect hunger, thirst, obesity, and eating behaviour. She has written a book called "Volumetrics Weight Control Plan: How to Feel Full on Fewer Calories" in which she explains her findings about water, weight loss, and feeling satisfied after eating.
It was once believed that our bodies have a hard time differentiating between hunger and thirst. So dieters were often told to drink a glass of water every time they feel hungry in between meals and to drink a glass or two of water before eating to keep their appetites under control.
But Rolls has discovered that hunger and thirst are two separate and distinct mechanisms. A liquid (water or another beverage) will quench your thirst but will not satisfy your hunger. She explains, "Water sneaks right past without triggering satiety signals, the cues that tell your body when you're full".
Water can still help you lose weight if you drink it instead of a soft drink or another high-sugar beverage because water contains zero calories but it won't take the edge of your hunger.
Not all liquids are the same though. Rolls has found that milk-based drinks and drinks with some protein in it will help you feel full and eat less at the next meal. The reason is because milk turns into a semi-solid food in the stomach and research has found that protein keeps you satisfied longer than fat or carbohydrates. That's why toddlers who drink too much milk don't have any appetite to eat their food.
How to eat your water.
While drinking water with your meals does not help much at keeping hunger at bay, Rolls has found that eating water or incorporating water into your food has a significant impact in helping you eat less.
In a Penn State experiment published in The American Journal of Clinical Nutrition, Rolls found that women who were given a bowl of chicken and rice soup felt fuller and ate less than those who were given a chicken and rice casserole and a glass of water even though both meals contained exactly the same ingredients, calories, and amount of liquid.
In an interview with Bonnie Liebmann of Nutrition Action Health Letter, Rolls speculates that the women may have been less hungry after the soup because it looked more like food even though it was watery plus it looked bigger in volume than the casserole did. She says this probably satisfied their brains as well as their stomachs since we all have a predetermined notion of what an "appropriate" portion looks like to keep us feeling full. Another possibility is that "when you drink water on the side, it's processed by thirst mechanisms, while soup is processed by hunger mechanisms".
Volume of food directly linked to
Soup is not the only way to eat your water. In other experiments at Penn State, Rolls and her research team found that eating foods with a high water content - like fruits and vegetables - can help people to feel full and satisfied on fewer calories. Rolls believes this is because water in food leaves the stomach more slowly than just plain water.
Her research has shown that the volume of food you eat is directly linked to how full you feel after a meal. As soon as the volume of food in your stomach reaches a certain size (it's different from one person to the next), certain sensors in your stomach tell your brain that you are full. Of course there are many other factors involved that tell you when to stop eating but volume of food seems to be a major player in that decision.
Rolls further discovered that when the participants in her studies were allowed to serve themselves, they would eat the same weight of food on most days. They were satisfied with a particular volume of food and it did not matter whether the food was low or high in calories. It was simply the bulk of the food that kept them feeling full after the meal.
Food that is bulky but low in calories is called a low energy density food. It has a small amount of calories in a large serving. It usually contains a high amount of water and fiber and is low in fat. An example would be a medium-sized orange, which has approximately 60 calories.
A high energy density food has a lot of calories in a small serving. It usually has a lower water and fiber content and a higher fat content. An example would be a tablespoon of mayonnaise, which has about 100 calories.
In her book, Volumetrics, Rolls compares
raisins and grapes to better explain the energy density concept. A 100-calorie
serving of raisins is one-fourth of a cup while a 100-calorie serving of
grapes is one and two-thirds cups. Since the raisins are so light in weight,
you will tend to eat much more of them before you are full.
Here are two more examples. To get the same amount of calories in just ten jellybeans (100 calories), you would have to eat two cups of strawberries. One cup of strawberries is already quite filling (50 calories) but ten jellybeans won't even make a dent in your stomach.
Ten pieces of Hershey Kisses has 250 calories while an eight-ounce glass of chocolate milk has 250. The chocolate milk will satisfy your chocolate craving and fill up your stomach at the same time.
Here's a Pinoy example. Ten soda crackers is equivalent to approximately 400 calories. Believe it or not, but you could have a satisfying meal of ½ cup steamed rice, inihaw na bangus (the size of a deck of cards), a cup of kangkong, and cup of cantaloupe for about 378 calories.
General guidelines and practical
By eating food that is high in water and fiber, you can lose weight without starving or depriving yourself. In her book, Rolls gives some general guidelines: Eat more foods that are naturally rich in water, such as fruits, vegetables, low-fat milk, and cooked grains, as well as lean meats, poultry, fish, and beans. Eat more water-rich dishes like soups, stews, casseroles, pasta with lots of vegetables, and fruit-based desserts.
On the other hand, be careful about foods that is very low in water: High-fat foods like potato chips, but also low-fat and fat-free foods that contain very little moisture, like pretzels, crackers, and fat-free cookies.
As much as you can, add vegetables to your favorite recipes to increase bulk without adding too many calories. Instead of having a cup of pancit with a sprinkling of veggies, have half a cup of pancit with a cup or more of vegetables. Put more eggplant than pasta in your lasagna. Put more vegetables in your casseroles like kare-kare and your soups like tinola or sinigang. Make filling "cream" soups with pureed vegetables and non-fat milk. Make your sandwiches bulkier by adding more slices of tomato and lettuce.
How to calculate energy density.
If Rolls has her way, in the future, nutrition labels at the back of food products will contain an energy density rating. For now, you can calculate it yourself by looking at how many calories there are per serving and how many grams a serving weighs (remember that you are looking for grams in weight, not carbohydrate or fat grams). Calories divided by grams equals energy density.
Foods very low in energy density (less than 0.6): Most fruits and vegetables, skim milk, and broth-based soups.
Foods low in energy density (0.6 to 1.5): Many cooked grains, breakfast cereals with low-fat milk, low-fat meats, beans and legumes, low-fat mixed dishes and salads.
Foods medium in energy density: (1.5 to 4): Meats, cheeses, high-fat mixed dishes, salad dressing, some snack foods.
Foods high in energy density (4 to 9): Crackers, chips, chocolate candies, cookies, nuts, butter, and full-fat condiments.
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