When the bacteria have finished and their bodies have been incorporated into the waste, the feces — small remains of yesterday’s copious feast — pass down through your rectum and out through your anus. But not necessarily right away: Digestion of any one meal may take longer than a day to complete.
PREBIOTICS AND PROBIOTICS: THE GOOD GUT TWINS
A little more than 100 years ago, Ilya Ilyich (Elie) Metchnikoff, a Russian scientist, decided that humans who died young had succumbed to the effects of “putrefying bacteria” in their intestines. Searching for a remedy, Metchnikoff ended up with Bulgarian peasants, a significant number of whom lived well into their late 80s. Historians may argue that the only way to have lived long in Bulgaria was to avoid Bulgarian politics, but Metchnikoff credited the national longevity to yogurt, the first time someone recognized the benefits of probiotics, a discovery that won him the Nobel Prize in physiology and medicine in 1908.
The National Institutes of Health (NIH) defines probiotics as “live microorganisms that are similar to the beneficial microorganisms found in the human gut.” The most common probiotics in our food are members of the Lactobacilli family, such as the ones in Metchnikoff’s magic Bulgarian yogurt. Probiotic microbes are also active in other fermented food, including kefir, tempeh, some pickles, sauerkraut, and kimchi. (Note: Heat kills these microbes, so to be useful they must be live as noted on the labels for many yogurts.) Recently, a new term has entered the conversation: prebiotics. As you can assume, the “pre” means something that comes before probiotics — in this case, dietary fiber your body cannot absorb but which serves as food for those protective probiotic microbes. (See Chapter 8 for more on dietary fiber.)
While food is your best natural source of prebiotics and probiotics, the hot market right now is in supplements: probiotic tablets, capsules, powders, lozenges, and gums whose worldwide sales are expected to rise from $2.5 billion in 2018 to an astronomical $74.69 billion by 2025. And no wonder. Healthwise, proponents claim a slew of benefits for probiotics, including the prosaic but highly welcome ability to prevent or ease diarrhea due to an infection or treatment with antibiotics that wipes out normal bacterial colonies in the intestines. In 2014, a metanalysis for 24 different trials showed that probiotics also helped prevent a life-threatening intestinal inflammation in newborn premature infants.
Some studies also suggest that probiotics may alleviate symptoms of digestive disorders such as irritable bowel syndrome (IBS) and improve and perhaps relieve depression, but no evidence supports claims that they strengthen your immune system or make it easier for you to lose weight. And there’s this: Probiotic products are supplements, which means the Food and Drug Administration (FDA) regulates them as food, not drugs, so they don’t have to prove that they’re safe or effective. (See Chapter 13 for more on supplement safety.) That matters because with all the hoopla surrounding a “natural” product, there is a clear lack of data regarding the possible risks of long-term use of these supplements.
The bottom line: Probiotics are a promising field of research, and one day they may be used to treat or help prevent many disorders. But right now, not enough evidence exists to recommend their widespread use.
Chapter 3
How Much Nutrition Do You Need?
IN THIS CHAPTER
A healthful diet provides sufficient amounts of all the nutrients that your body needs. The question is, how much is enough?
Today, three sets of recommendations provide the answers, and each one comes with its own virtues and deficiencies. The first, and most familiar, is the RDA (short for Recommended Dietary Allowance). The second, originally known as the Estimated Safe and Adequate Daily Dietary Intakes (ESADDI), now shortened to Adequate Intake or simply AI, describes recommended amounts of nutrients for which no RDAs exist. The third is the DRI (Dietary Reference Intake), an umbrella term that includes RDAs plus several innovative categories of nutrient recommendations: EAR (Estimated Average Requirement), AI (Adequate Intake), and UL (Tolerable Upper Intake Level).
Confused? Not to worry. This chapter spells it all out.
RDAs: Guidelines for Good Nutrition
The Recommended Dietary Allowances (RDAs) were created in 1941 by the Food and Nutrition Board, a subsidiary of the National Research Council, which is part of the National Academy of Sciences in Washington, D.C., in order to investigate issues of nutrition that might “affect national defense.” The committee was renamed the Food and Nutrition Board in 1941, after which they began to deliberate on a set of recommendations of a standard daily allowance for each type of nutrient. The standards would be used for nutrition recommendations for the armed forces, for civilians, and for overseas populations who might need food relief.
RDAs originally were designed to make planning several days’ meals in advance easy for you. The D in RDA stands for dietary, not daily, because the RDAs are an average. You may get more of a nutrient one day and less the next, but the idea is to hit an average over several days.
For example, the current RDA for vitamin C is 75 milligrams for a woman and 90 milligrams for a man (age 18 and older). One 8-ounce glass of fresh orange juice has 120 milligrams of vitamin C, so a woman can have an 8-ounce glass of orange juice on Monday and Tuesday, skip Wednesday, and still meet the RDA for the three days. A man may have to toss in something else — maybe a stalk of broccoli — to be able to do the same thing. No big deal.
The amounts recommended by the RDAs provide a margin of safety for healthy people, but they’re not therapeutic. In other words, RDA servings won’t cure a nutrient deficiency, but they can prevent one from occurring.
Proteins, vitamins, and minerals: The essentials
RDAs offer recommendations for protein and 18 essential vitamins and minerals. For the specific amounts, check out Chapter 6 (protein), Chapter 10 (vitamins), and Chapter 11 (minerals).
Recommendations for carbohydrates, fats, dietary fiber, and alcohol
What nutrients are missing from the RDA list of essentials? Carbohydrates, fiber, fat, and alcohol. The reason is simple: If your diet provides enough protein, vitamins, and minerals, it’s almost certain to provide enough carbohydrates and probably more than enough fat. Although no specific RDAs exist for carbohydrates and fat, guidelines definitely exist for them and for dietary fiber and alcohol.
In 1980, the U.S. Public Health Service and the U.S. Department of Agriculture joined forces to produce the first edition of Dietary Guidelines for Americans (see Chapter 16). A new edition of the Dietary Guidelines has been issued every five years since then to set parameters for what you can consider reasonable amounts of calories, carbohydrates, dietary