DEAR DR. BLONZ: I have a question about calories in carbohydrates, protein and fat. After a meal, do we gain weight or fat immediately, or does this happen overnight? I’ve never seen a good answer to this question. -- P.E., Walnut Creek, California
DEAR P.E.: We weigh the most right after we eat and drink. Assuming you don’t chow down right before you nod off, or wake up in the middle of the night to raid the refrigerator, you actually lose weight as you sleep.
Calories are a measure of potential energy. They can come in the form of fat (9 calories per gram), carbohydrate and/or protein (4 calories per gram), and even alcohol (7 calories per gram). The calories in any particular food represent its potential energy to fuel work and other metabolic processes, much in the same way that money in its different forms can be thought of as financial “energy” that can be used to buy objects or pay for services.
Once consumed and absorbed, dietary energy becomes a part of the body’s general energy pool, a resource that goes wherever it’s needed. There are certain functions that carbohydrates can perform that fats cannot, and there are those unique to certain types of dietary fats and the amino acids found in protein. Focusing solely on energy, we can say that non-fat calories get turned into glucose, and a small amount gets stored in the liver and muscles as glycogen. The body needs to keep blood glucose within specific limits, so extra glucose quickly gets converted to fatty acids and packaged for transport to storage under the skin and in our hips, thighs, and all those other places. This can take place in a matter of hours after a meal.
The blood is the great highway that carries these energy substances in every direction. Blood is water-based, so there are upper limits to how much fat (lipid) can be tolerated. Much gets packaged into substances known as lipoproteins. For those in good health, as the blood fats/lipids rise, more will get pulled out of the blood and put into storage on your waistline (or wherever else you don’t want it). If you have ever had your blood drawn soon after a big meal, you may have noticed that the blood takes on a milky appearance. This type of blood is described as lipemic, reflecting all those lipids from the meal that are still in the blood.
In the hours after we eat, the net flow of energy compounds is from the digestive system to the blood, with the excess finding its way into storage as fat. The ongoing energy dynamic will always be based on demands at the moment. If, for example, you go out for a walk after a meal, fats/lipids originally destined for storage can get pulled out of the blood to fuel muscular work rather than completing their original journey.
What about gaining fat overnight? After you eat, all the fat from the meal is there, but additional fat can be formed from excess carbohydrates, protein and alcohol calories. If the fat synthesized while you snooze is greater than that needed to keep your body running, you can wake with more fat in your body than when you went to sleep.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.