foods. Not all of the nutrients that come from food and supplements get absorbed in the same place; they’re absorbed throughout your GI tract. Here are the rest stations where nutrients are absorbed:
Stomach: alcohol
Duodenum (first part of the small intestine; takes off from the stomach): calcium, magnesium, iron, fat-soluble vitamins A and D, glucose
Jejunum (middle part of the small intestine): fat sucrose, lactose, glucose, proteins, amino acids, fat-soluble vitamins A and D, water-soluble vitamins like folic acid
Ileum (last part of the small intestine; leads to large bowel): proteins, amino acids, water-soluble vitamins like folic acid, vitamin B12
Colon (also known as the large bowel): water, potassium, sodium chloride
FACTOID
The average person has 10,000 taste buds, which are onion-shaped structures. People regenerate new taste buds every three to ten days, but these regenerate at a slower rate as people get older. Elderly people may have only 5,000 taste buds.
Here’s how the system starts: Before a morsel even reaches the tollbooth, your body has a radar gun to let you know that food is coming—powered by such physiological cues as sight, smell, and the fact that you’ve been drooling like an overheated Saint Bernard at the thought of a fried-cheese appetizer special. In response to that sensory information, glands in your mouth start to secrete enzymes to help break down your food; then your stomach quickly constructs its version of a roadside welcome center by pumping out stomach acid to help prepare your body for the digestion process.
Now, don’t underestimate your stamp licker as a player in this digestion process. Back in the day of buffalo-hide cocktail dresses, people relied on their tongues (and their noses) for survival; if it tasted good, then it was safe, and if it tasted like dinosaur dung, then it could be poisonous or toxic.
FACTOID
Maybe the old days were right: It used to be that young docs would criticize older docs for giving B12 shots, calling them nothing more than placebos. But nearly 40 percent of Americans may suffer from a vitamin B12 deficiency.
We do the same things, but in slightly different ways. Since our bodies use our senses to process information, we rely on our tongue for information about food. The information we acquire sends messages to the brain, and then the brain sends messages to our forks: keep eating or stop eating. That message largely comes from our five tastes (sweet, sour, salty, bitter, and unami, which recognizes the inherent deliciousness in foods like juicy filet mignon), but it also comes from what we smell. Some researchers say that three-quarters of how we “taste” certain foods actually comes from how we smell it. What’s this have to do with your waist growing? For one, there’s the obvious: the more you like a bad-for-you food, the more likely you are to keep eating it. But the genetics of taste and taste buds may play an even more subtle and fascinating role. As you’ll see in the box on page 70 (“Are You a Supertaster?”), the physiological makeup of your tongue could make you more or less disposed to eating good or bad foods.
Figure 3.2 Taste Tester The most powerful muscle in the body, the tongue, tastes food with papillae that sense the chemicals in foods and tell you whether they’re worth your continued attention.
Figure 3.3 Chewing the Fat One of the reasons we can gain weight so readily is the efficiency of our teeth, which fit perfectly with one another to ensure that every morsel of food is crushed completely. Salivary glands near the lower teeth and at the back of mouth secrete enzymes to hasten digestion before swallowing. The sight and smell of food warn these systems of what’s to come.
FACTOID
Eating nuts does not create the calorie intake that you might expect because 5 percent to 15 percent of the calories are not absorbed by the intestinal system. That’s because the nuts’ skin and how well we chew nuts influence digestion. An added bonus: The slow release of calories throughout the intestinal system leads to prolonged satiety.
Unlike other animals, we waste very little energy eating because of our highly efficient perfectly opposing molars (see Figure 3.3). The powerful crushing motion helps us extract every possible calorie from the prime rib deluxe. Other animals waste or burn a lot of calories while they eat because their teeth do not efficiently mush the food when they move prey to belly. In humans, once that food actually does breeze past the toll booth, it accelerates onto the on-ramp of the esophagus—that’s the tube that links your mouth to the interstate that is your GI system.
After your Double Whopper slides down the on-ramp, it has to make a tricky merge in the form of a sharp turn to enter the stomach. That angle—the gastroesophageal junction—is what keeps stomach acid from spilling back into your esophagus and making your chest feel like an arson victim. (When you have extra fat in your belly, that angle is pried open, allowing acid to spill upward and cause heartburn. See “The Word on Gerd,” page 64.) Once your Whopper chunks have entered your stomach, serious digestion begins. The food is held in your stomach until your body directs it to the small intestine, where most of the nutrients are absorbed and passed along to the rest of your body through your bloodstream (to the liver, which is the next stop for absorbed nutrients), or to the large intestine on the way to evacuation.
Food Processor:
How Your Body Breaks Down Nutrients
In terms of weight gain, a calorie is a calorie is a calorie. Calories not used immediately by your body for energy are either eliminated as waste or stored as fat. YOU-reka! But that doesn’t mean that all calories are treated equally by your body. For example, protein and fiber with high water content have a great effect on satiety, and simple carbohydrates have the least effect on satiety. (Fat, by the way, has an effect on satiety similar to that of protein and fiber, which is why low-fat diets leave people hungry all the time.) When it comes to converting calories, your body processes fat most efficiently—meaning that you actually keep more of it, because your body doesn’t need to expend as many calories trying to store it. On the flip side, your body works hard to process protein, to make it highly flammable to your body’s metabolic furnace.
Oh, the Gall
Your gallbladder may seem as unnecessary as bad goatees, but one of its functions is to help store bile-that digestive juice that helps your body absorb nutrients. Obese people have a greater than 50 percent chance of developing gallstones. Why? An overworked liver caused by being overweight makes bile, which is more like sludge than liquid, and predisposes them to developing stones. It’s also more likely that you’ll develop stones when you lose weight fast, like after weight-loss surgery-because the gallbladder doesn’t empty enough when it doesn’t see any fat. So it’s not uncommon for a surgeon to remove the gallbladder during a gastric bypass procedure. The risk factors for developing the painful stones are easy to remember, because they sound like an R & B group. They’re the 4 Fs: female, fertile, fat and forty. (We don’t mean this to be a gender issue, but the fact is that women are more likely to have gallstone symptoms than men.)
Contrary
