When it comes to a healthy diet, it’s not just what you eat—it’s when you eat it, and even how you store it. Clever tricks for optimizing ingestion…

1 WHICH VITAMINS SHOULD YOU NEVER TAKE AT NIGHT?

Vitamin C not only supports the immune system—it also stimulates the production of norepinephrine, a neurotransmitter that’s responsible for alertness, vigilance, and the body’s fight-or-flight response. That’s why vitamin C, when ingested at night, can have an impact on the quality of sleep or even trigger insomnia. Vitamin D also has a stimulating effect because it promotes production of the “happy hormone” serotonin, preventing the release of the hormone melatonin that helps regulate the sleep-wake cycle.

2 WHY SHOULD YOU LET NOODLES REST OVERNIGHT?

Freshly cooked noodles are mostly carbohydrates in the form of polysaccharides. Like other carbohydrates, they are primarily digested in the small intestine with the help of enzymes secreted from the pancreas (amylase) or by the cells that line the small intestine (enterocytes). They convert the carbohydrates into simple sugars, raising blood sugar levels and triggering a rush of insulin that soon makes you feel hungry again. But a simple trick can prevent the spike: Letting pasta cool after you cook it changes its structure to create a different kind of starch, one that is more resistant to intestinal enzymes. When you eat it, the glucose peak is smaller and the body absorbs fewer calories. If the leftover pasta is reheated before you eat it, the starch becomes even more resistant, and the rise in blood sugar is even lower. The undigested starch then travels to the large intestine, where it nourishes some of the beneficial bacteria that live there. But always put pasta in the fridge for storage: Noodles stored at room temperature can develop dangerous pathogens.

3 WHAT MAKES MICROWAVING A BETTER CHOICE THAN STOVETOP COOKING?

You’ll often hear that microwave cooking destroys vitamins, but that’s an urban legend. In truth the electromagnetic waves do nothing more than make water molecules in the food vibrate as they absorb radiation, thus heating up the food around them. They do not damage the vitamins in the food, although some vitamins (such as B1, B12, and C) are destroyed by heat in general. Cooking temperature and duration affect vitamin content, so microwave cooking is often a better choice. An additional advantage: Because microwave cooking doesn’t involve boiling the food in water, vitamins are not leached out and discarded with the cooking liquid. Cooking times are also shorter since the heat is generated inside the food instead of having to penetrate it from the outside.

4 HOW CAN YOU PRESERVE THE VITAMINS IN FOOD?

Fruits and vegetables can quickly lose important nutrients. The loss of vitamin C in vegetables stored in the fridge for seven days ranges widely: 15% for green peas and 77% for green beans, for example. Broccoli fares better: It loses no vitamin C after seven days in the fridge. And refrigeration is crucial: Broccoli stored at 68°F loses 56% of its vitamin C in the same period, becoming yellow and wilted. The best way to prevent the nutrient loss that starts right after harvest is to freeze fresh vegetables immediately.

5 WHEN IS A BELL PEPPER A-SUPE-LEMON?

Green bell peppers are cheaper than yellow or red ones because they are not allowed to ripen (and thus require less time from planting to harvesting). The green color is the result of the same chlorophyll found in the plant’s leaves, and it masks the other colored pigments as long as it is present in sufficiently high quantities. It takes about three weeks for this member of the nightshade family to change color to yellow, orange, red, or purple. Those colors are the result of carotenoids, a group of tetraterpene pigments. While the peppers are changing color, their vitamin C content is rising rapidly. A half-cup serving of green bell pepper contains 60 mg of vitamin C while red bell pepper contains nearly 50% more. In both cases that’s considerably more than the amount of vitamin C found in the juice of a medium lemon. But that’s not the only way bell peppers improve health. Carotenoids are antioxidants that help the body fight cancer. They also have anti-inflammatory properties and boost the immune system. And some are converted to vitamin A, which promotes good vision. Incidentally, a bell pepper is actually a fruit and not a vegetable.

6 IS THERE A FOUNTAIN OF YOUTH FOR POTATOES?

The colorless, flammable gas ethylene is actually a hormone that makes fruits and vegetables ripen. Apples begin to emit ethylene as soon as they’re ripe, and when other fruits or vegetables come into contact with ripe apples, they start producing ethylene as well. That speeds up the ripening process. The exception is potatoes: If you store an apple with a 5-pound sack of spuds, for example, the ethylene it gives off has the opposite effect. Studies have shown that even a small amount of the hormone actually makes potatoes keep much longer in extended storage.

7 WHICH VEGETABLES GET HEALTHIER THE LONGER THEY’RE COOKED?

Generally speaking, vegetables lose nutrients as you heat them. Vitamin C, for example, suffers at temperatures as low as 86°F, and the negative effect increases as the temperature rises. And cooking water leaches out vitamins, which are then lost when the water is discarded. But these principles do not apply to tomatoes and carrots, which are virtually impossible to overcook. The longer the cooking time, the more bioavailable the lycopene in tomatoes and the beta-carotene in carrots becomes.

8 DO FOODS KEEP FOREVER IN THE FREEZER?

In 1912 the young American biologist Clarence Birdseye went to northeastern Canada to trade in fox furs. There he observed the Inuit people using extremely low temperatures to preserve fresh fish and noted that freezing did not affect its appearance, texture, or taste. Returning to the U.S. in 1917, he went into the frozenfish business, and five years later he established company to market flash-frozen fish, meat, and vegetables. By the end of the 1940s many American homes were equipped with freezers, and soon other companies were offering frozen foods, including pizzas and complete meals. The age of frozen convenience foods had begun. But while foods stored at a temperature of 0°F can indefinitely be kept safely, that doesn’t mean the quality won’t start declining over time. The food-safety chart at foodsafety.gov does not recommend storing any food in the freezer for more than a year, and for some foods (bacon, ham) the optimal storage period is no more than a month. Water accounts for about 90% by weight of most fruits and vegetables. It’s held within cell walls that provide texture and structure. When the water freezes, it expands, rupturing the cells. Thus it is important to freeze food as fast as possible to prevent the formation of large ice crystals. Tip: Set the freezer to its lowest temperature in advance, and don’t freeze too much food in a single batch.

9 SHOULD FRUIT ALWAYS BE EATEN FRESH?

Ounce for ounce, dried fruit has more minerals and dietary fiber than fresh fruit and also contains more antioxidants. Fiber helps fight obesity and heart disease and may help prevent some kinds of cancer. Antioxidants are believed to reduce the likelihood of diabetes. Because water content has been removed from dried fruit, other components exist in a concentrated form, and if the fruit was freeze-dried, more vitamins will remain than if heat was used to desiccate the fruit. Dried fruit can also boost metabolism.

10 HOW DOES THE 30-SECOND CRACKER TEST WORK?

Researchers have discovered some people metabolize carbohydrates better than others. Are you one of them? Try the 30-second cracker test to find out: Fill your mouth with saliva and chew an unsalted cracker, using a stopwatch to see how long it takes for the cracker to change taste. It should become sweeter as the carbohydrates break down in your mouth. If that happens in less than 30 seconds, you have a high concentration of the necessary enzyme amylase and can digest carbs without significant weight gain. If it takes longer or you notice no change at all, you’re more likely to gain weight from eating carbs.

11 SHOULD YOU PUT APPLES IN THE FRIDGE ASAP?

Apples are generally harvested only when they’re ripe, and some species lose their crispness if they’re stored at room temperature for more than a few days. Put apples in the coldest part of the fridge, and keep them away from foods with a pronounced odor. Even in the fridge, some apple species soon lose their crispness while others will stay fresh for weeks or even months. Because the ethylene gas they produce promotes spoilage, it’s better not to store them in a plastic bag or next to sensitive produce.

12 CAN OLD BREAD BE REVIVED?

Per capita, Americans consume an average of 53 pounds of bread per year. Of all the bread produced in the U.S. each year, an estimated one-third of it goes to waste, discarded at home or in the store because it has passed its best-by date. We tend to get rid of bread when it has lost so much moisture that it seems dry. However the taste and freshness can be restored; all you need to do to achieve rejuvenation is dampen the bread on all sides before toasting it in the oven for 5 minutes at 300°F. Some of the added moisture penetrates the interior while the rest is evaporated by the heat—and old bread suddenly seems fresh again.

13 HOW DOES THE LOCATION IN THE FRIDGE AFFECT THE STORAGE LIFE OF FOODS?

Most refrigerators have various climate zones that range from about 35°F at the bottom to 40°F or so in the middle to about 45°F at the top. The vegetable bin and the refrigerator door are the warmest places in the fridge, where the temperature can be as high as 50°F. Foods that spoil easily, such as fish and meat, should always be stored at the bottom of the fridge, and cheese and ready-to-eat foods toward the top. The refrigerator door is the best place for beverages and condiments.

14 CAN BANANAS KEEP ILLNESSES AT BAY?

A banana’s color can tell you more than just how ripe it is—color also indicates the effect the fruit will have on the body. All bananas are high in potassium, an electrolyte that reduces the risk of heart disease. They also supply magnesium, fiber, folate, and vitamins such as B6, B12, and C. Green bananas also contain resistant starch that may lower blood pressure and cholesterol levels as well as help to regulate blood sugar levels. Ripe bananas that have dark spots enhance the power of white blood cells to fight off infections caused by viruses, bacteria, and fungi.

15 HOW SOON SHOULD YOU REFRIGERATE LEFTOVERS?

Leftover food can make for a tasty meal but also a dangerous one if the food has been stored at room temperature. That allows bacteria to grow, including strains that cause food poisoning. To ensure food stays safe to eat, put leftovers in the fridge or the freezer within two hours after cooking. In hot weather, do it within an hour. In one survey, one-third of respondents admitted to eating pizza that had been left out overnight. Don’t do that! Also, it’s not necessary to let food cool all the way to room temperature before refrigerating it.