OFF the coast of Peru swim billions of sardines and anchovies: oily, smelly little fish, rich in nutritious omega-3 fatty acids. Their spot on the food chain is low; many will be caught, ground up, and fed as fishmeal to bigger animals.

But a few have a more exalted destiny: to be transported, purified and served at North American breakfast tables in the form of Tropicana Healthy Heart orange juice and Wonder Headstart bread. These new products promise to deliver the health benefits of fish oil without the smell and the taste — without, in fact, the fish.

The possible benefits of eating omega-3s include cardiovascular protection and improved neural development in children.

However, “People just aren’t eating salmon or sardines twice a day,” said Ellie Halevy, director for marketing of Tropicana, which is owned by PepsiCo. “But they will drink two glasses of orange juice, if it has no fishy taste and all the benefits.”

Orange juice laced with anchovies is one example of the latest way major food companies are competing for health-conscious consumers: plugging one food into another and claiming the health benefits of both. Shoppers are offered green tea extracts in their ginger ale, yogurt bacteria in their salsa, and powdered beets in their peanut butter. Market staples like blueberries (high in certain antioxidants), cherries (may have anti-inflammatory benefits) and bananas (when unripe, particularly rich in fiber) are being broken down, shaken up, microencapsulated, and put to work in new ways.

These additives are often called nutraceuticals, broadly defined as ingredients that are derived from food, and that offer health benefits associated with that food. Nutraceuticals like garlic pills and cranberry capsules became popular in the 1990s, usually taken alone in the form of dietary supplements.

Now Kraft, Dannon, General Mills and many other companies are adding nutraceuticals to existing foods: “fat-burning waffles” made from a newly developed corn flour, cheese that kills intestinal parasites, even ketchup that regulates digestion, are on the shelves or in the works. New technologies in food processing, and a landmark 1999 court decision giving the makers of supplements broad leeway to advertise their health benefits, have brought this new class of enhanced foods to supermarket shelves.

These products are known as functional foods, meaning they have been modified to make them more nutritious, like genetically modified rice or fortified milk.

“One day, we believe, you will be able to walk into a supermarket and all the products could be enriched with omega-3s: milk, yogurt, tortillas,” said Ian Lucas, head of marketing for Ocean Nutrition Canada, maker of the fish oil used by Tropicana.

Are we really that close to a world in which food functions as a nutrient delivery system, made possible by microencapsulation and fine-spray coating? And what would this mean for food and human nutrition?

“This whole area is far more complex than we thought just one or two years ago,” said Alice H. Lichtenstein, a professor of nutrition science and policy at Tufts University.

Since the 1970s, as nutrition research has progressed beyond “vitamins and minerals,” a variety of new compounds have been touted as the key to health: antioxidants (related to vitamins, these include lycopene, beta-carotene and other plant-based nutrients); long-chain fatty acids like omega-3s, plentiful in fish and some plants; and “probiotics,” the live bacteria in yogurt and fermented vegetables.

There is significant scientific agreement — the standard the Food and Drug Administration requires before foodmakers can place unqualified health claims on packaging — on the benefits of certain nutrients, including calcium, fiber, folate, soy protein, omega-3 fatty acids, lactic acid bacteria and a few others. In food, these have proved to help protect against specific diseases (calcium against osteoporosis, omega-3 fatty acids for heart disease), and many nutritionists believe that they are beneficial in supplement form.

However, recent studies on supplemental vitamin E, beta-carotene and folate (all of which fall into the broad category of “antioxidants”) surprised everyone by showing no benefits whatsoever for cardiovascular disease. “There is a great deal we don’t know about how the compounds in food are made available to the body,” Dr. Lichtenstein said. “Now we have to be more cautious about individual nutrients, though we should not close our minds, given the successes of the past.”

Fortified food is certainly one of the great triumphs of public-health policy. When vitamin-B-enriched flour was introduced in the 1940s, rates of pellagra plummeted. Iodine-fortified salt virtually wiped out goiter, and vitamin-D-enriched milk eliminated rickets in children. But some experts say that such carefully designed campaigns have little in common with the fortified products now turning up in supermarkets.

“Those decisions were based on rigorous public-health studies,” said Dr. Jeffrey Mechanick, a professor of endocrinology at Mount Sinai School of Medicine. “But the science hasn’t been done on the new nutraceutical products, and the F.D.A.’s current labeling standards are inadequate.”

The agency does not have specific rules for the labeling of functional foods. “It all depends on what type of claim is being made,” said Michael Herndon, an agency spokesman. “An unqualified health claim like ‘calcium reduces your risk of osteoporosis,’ has to be proved in advance. A more general claim like ‘X keeps your heart healthy’ has to be provable by the manufacturer, but we would not require proof in advance.” As with conventional foods, functional foods must clearly state the presence of allergens, like milk or fish, in the ingredients list.

The Food and Drug Administration does not conduct nutritional research. Several other federal agencies do so, but functional foods are not evaluated by any specific office. “Nutraceutical products have characteristics of both food and drugs,” said David A. Kessler, a former commissioner of the F.D.A. “It’s easy for them to slip through the cracks, and the industry is always ahead of the agency.”

The free-market policy on claims for nutraceuticals benefits companies like LycoRed, a global provider of compounds pulled out of tomatoes that grow in desert greenhouses in Israel. LycoRed, like FutureCeuticals, National Starch, the German chemical giant BASF and other companies, produces a range of additives for the food industry.

“Everybody already knows that a tomato is healthy,” said Udi Alroy, the company’s chief marketer. “We don’t have to sell something from Mars.” But the form in which the tomato appears in LycoRed products is somewhat unearthly. Specially bred tomatoes, bright red and flavorless, are pulped and then treated to extract the valuable compounds of lycopene, beta-carotene and lutein — which are then encapsulated in “beadlets” so tiny they cannot be felt by the human tongue.

“People want their food to have the same organoleptic qualities, not be gritty or taste different or feel weird,” said Kevin Stark, head of the food technology division of NineSigma, a research company that helps put clients like General Mills and Procter & Gamble in touch with scientists and technologists around the world.

The tiny capsules, made of fat, protein or sometimes plastic, can be designed to deliver foods to a particular part of the digestive tract. Some capsules can wait out long periods on shelves or even survive heat treatment, the method used to cook and sterilize most canned foods.

Other new technologies can remove the fishy smell of fish, distill a pomegranate into flavorless powder and possibly deliver the nutritional benefits of a green bean via a slice of pound cake, and major players like Dannon, Nestlé and PepsiCo are plunging in.

A new brand of peanut butter, Zap, is imperceptibly fortified with powdered beets, carrots and bananas. Nutritious Chocolate, a new product from Gary Null, a health-food marketer, includes the usual ingredients of chocolate: cocoa butter, cocoa beans, cane sugar, vanilla. Oh, and broccoli, cranberries, nectarines, parsley, pomegranates, watermelons, kale and more — a total of 30 additional plants, all in powdered form.

But whether the nutritional benefits of the original foods survive in additive form is still to be determined.

“Whether a tomato is good for you, that’s one thing,” Dr. Kessler said. “Whether the lycopene in a tomato is good for you, that’s another. And then whether synthetic lycopene and microencapsulated lycopene are also good for you, that’s yet another thing.”

In a manufacturing plant outside Paris, the Danone Group, parent company of Dannon, nourishes more than 3,000 different strains of lactic acid bacteria for its lines of “probiotic” yogurts. All yogurt is fermented with live cultures, but Danone claims to have harnessed yogurt’s healing potential to particular ends. “Different strains work for different problems,” said Miguel Freitas, Dannon’s scientific affairs director. “The one for Activia works on slow transit” — the company’s elegant term for constipation — “and the one for DanActive on immunity.”

Tropicana offers an orange juice tailored for bone loss, another for acid reflux, and one for weight loss. Many factors are pushing this trend toward health-specific foods: the aging population, changes in labeling rules, the general trend toward micromarketing that makes consumers accept, and soon expect, 12 slightly different Tropicana orange juices on the shelf where one used to be enough for everyone.

Additionally, with recent rising costs in raw materials, flavorings and transport, many food companies are refocusing their research and development; instead of adding expensive ingredients like sun-dried tomatoes or honey-roasted almonds to existing products, the search is on for inexpensive “value-added” products that customers will pay extra for. Mars’s CocoaVia line of chocolate claims to offer health benefits because of high levels of antioxidants; an ounce of CocoaVia blueberry almond chocolate costs about $1.25, while an ounce of the same manufacturer’s Dove blueberry almond chocolate costs about 75 cents. In order to get the nutritional benefits from CocoaVia, the company recommends eating two bars a day — an investment of more than $700 and 4,000 fat grams in the course of a year.

Eating the right nutrients is a complicated question, one that nutritionists say could most easily be solved by eating a wide range of basic foods.

Dr. Lichtenstein of Tufts says that the recent setbacks and surprises in nutrition research have made her rethink the whole model of adding nutrients to the diet, despite the effectiveness of vitamin fortification.

“Maybe the true benefit of eating a lot of fish is that you are actually eating less of something else, like steak,” she said. “Maybe a subtraction model is the key. We have a long way to go to find out.”