Mom is best described as a stubborn health nut—when I was a kid, she'd rather have me burn off germs with a good, natural fever than take Tylenol. But one day this summer a fever hit her, and it didn't let up for nine days. When her home remedies weren't bringing relief, she went to a physician and discovered that her iron levels were severely low, so low that her immune system was down and open to a small bug, which wouldn't leave without a week of swigs of Floradix, a liquid iron supplement she'd used in the past for moderate upkeep or rare occasions like this.

There had never been an occasion so dire, and the cause came as a shock, even to her doctor. A few select foods—healthy foods in any other light (including herbal tea) —were in fact depleting her iron levels. This realization was overwhelming for her, not unlike legendary mathematician John Nash finding out he'd lost his mind, all the while thinking he was on the brink of brilliance.

Americans eagerly jump and sway between diets, adjusting to each political-environmental debacle and the latest nutritional findings. But whether you are vegetarian, carnivorous, vegan, or wheat-free, there are still core nutrient levels that your body needs to maintain, and one of the most common nutritional imbalances is iron deficiency. Affecting at least 20 percent of American women, this form of anemia is defined as "a chronic state of diminished hemoglobin" —the oxygen-transporting component of red blood cells— "caused by a lack of iron, or poor absorption of iron." This comes straight from nutritionist Dr. Linda Page's Healthy Healing, Mom's most dog-eared alternative health book.

Hardcore meat eaters may call vegetarians weak lettuce lovers, but few realize that red meat, although it builds muscle, is not actually any better a source of iron than greens.

Without enough iron, the body becomes fatigued—in extreme cases, to the point of compromised cognition and speech. But we all get tired, so without routine blood tests, many people don't even realize their iron levels are low until they get indirect symptoms like a fever, and by then levels are dangerously low. If the condition goes untreated, they can need blood transfusions.

Mom didn't get that far, but she was close. Before the summer, her run-ins with iron deficiency moderately waxed and waned but were ultimately maintained by Floradix. Her midwife had introduced her to the magic stuff during her pregnancy, when women are particularly vulnerable, but she first discovered she was anemic at age 14. This was in the 1960s, when kids were told to eat their spinach—remember Popeye the sailor? He nearly smoked the stuff through his pipe. It's no wonder he fancied a girl named Olive Oyl and adopted her daughter Swee'Pea; together, they align in an iron vortex of dark leafy greens, legumes, and extracted plant fat.

A common misconception comes with equating iron with protein. Hardcore meat eaters may call vegetarians weak lettuce lovers, but few realize that red meat, although it builds muscle, is not actually any better a source of iron than greens. Red meat also contains a different form of iron ("heme") that the body can over-absorb, as opposed to that found in dark greens ("non-heme"). When taking in spinach, our bodies can tell when we've had enough iron (the rest gets filtered out), but iron from meat gets absorbed much more quickly and doesn't stop; this is a possible cause of heart disease.

Many other unexpected foods can also deplete the body of iron: soda, cow's milk, chocolate, tea, and coffee. Anything with high tannins (tea) or caffeine content may lend a boost of energy and may even be nutritious in many ways, but ironically, for people prone to iron deficiency, large amounts of these foods and drinks can actually block cells from absorbing a full dose of iron. During the early stages of Mom's fever, I stressed that she drink tea with Echinacea, an herb thought to boost the immune system. Silly me. I might as well have given her cyanide.

While Mom lay on the couch with no concrete dietary recommendations from her doctor (he prescribed iron pills), she and I searched through alternative medical books and drafted a grocery list. In addition to spinach (most effective when eaten raw or lightly cooked), I searched the aisles for whole grains, brown rice, beets, almonds, dried fruit, bananas, oranges, pineapple, broccoli, green peppers, beans, cruciferous vegetables (like Brussels sprouts), and cultured foods like soy, kefir, and yogurt. If she weren't vegan, I would have also picked up eggs, seafood (especially clams or oysters), and organ meats like chicken livers. As well as iron-rich food, the body also needs food that will help it absorb the iron: those containing manganese, vitamin C, and potassium. Within a week, Mom was back to normal.

Most important, don't wait till a crash. Shuffle these items into a daily diet or at least give them some weekly spots. Feeling particularly low? Take a shot of Floradix, available in the supplement aisle at most health food stores, the nearest Whole Foods Market included. Its combination of highly soluble iron, vitamins B and C, and herbal extracts allow for an estimated 25-percent absorption rate over iron pills' 2 to 10 percent. As with any supplement, though, Floradix should not replace a healthy diet. However, Popeye-advised or not, it is good to have around.