Natick, Mass. -- There is a seriousness of purpose here in the Department of Defense test kitchen these days.

In a sprawling, 1960s-style building set alongside a lake in this Boston suburb, two men in lab coats and hair nets bend over a stainless steel table covered in pale orange food bars each the size of a pack of cards.

They're figuring out how to cram 2,100 calories into each bar, at the same time making sure the slightly sweet, grain-based rations will survive a drop from an airplane. The bars will be distributed as humanitarian aid, and might keep fleeing war refugees alive.

Over in the department where field rations are developed, there is a similar gravitas. Like anxious mothers, nutritionists wonder how the new Meals Ready to Eat (MREs) created for the troops in Iraq are going over. Are the soldiers eating?

In the U.S. Army Soldier Systems Center in Natick, where every recipe required to feed the 1.4 million people in the nation's armed services is developed, it's more than the standard worry a home cook has about a new dish. Military food scientists know that making sure a soldier is well-nourished is as important to winning a war as the right ammunition and a working gas mask. Food that doesn't taste good goes uneaten, compromising a soldier's health and performance. And the nutritionists know they also have to prevent battlefield anorexia, a condition where the stress of war dulls appetites to dangerous levels.

BIG CHANGE IN APPROACH
That's why the military's approach to feeding soldiers is radically different than it was a decade ago, with meals now tailored to the tastes of an ethnically diverse fast-food generation raised on tacos, teriyaki and Starbucks.

In 1991, when troops fighting the Gulf War tasted the first generation of the military's new field rations, the reaction was a fractured version of the don't ask, don't tell policy.

When the food scientists originally developed MREs, they didn't ask what the modern soldier might find appealing. But the soldiers told them -- and in no uncertain terms -- calling the field rations "Meals Rejected by Everyone." They tossed unopened brown plastic bags filled with casseroles and ham loaf into the desert, and had nicknames for the worst entrees, like the "four fingers of death." Translation: smoked frankfurters.

"We had kind of a father-knows-best mentality about the menus," said Gerald Darsch, joint project director for the Department of Defense's combat feeding program based here.

GIS' TASTES DRIVE THE MENU

Today, he says, everything is driven by soldiers' tastes. "Everything we create is war fighter-recommended, war fighter-tested and war fighter-approved, " he said.

Although soldiers are supposed to eat three MREs a day, they often don't. Soldiers on the move who find the MREs too difficult to prepare in the field or too bulky "field strip" their packs of food to make room for gear. And some units have reported having to cut back their rations to one meal a day as they wait for supplies to reach them. That makes what nutritionists put in each ration pack extremely important.

"We know food matters, especially on the front lines. What they eat has a very positive impact on mood, which has a positive impact on morale, which has a scientifically proven impact on performance," Darsch said.

Ever since the war in Iraq began, the MRE part of the program has been front and center. Each year, the military orders about 3 million of the 1 1/2- pound food packages from three commercial food manufacturers contracted to produce them. Since October, however, the order has doubled and the factories are on overtime. More than 48 million MREs are stockpiled in the warehouses of Kuwait.

VEGETARIAN OPTIONS
The new breed of MREs offers 24 entrees, including four vegetarian options like cheese tortellini and pasta Alfredo. The choices are geared to a more diverse fighting force that has a strong preference for spicier ethnic food. Some MREs feature Thai chicken, Jamaican pork chops or a gloppy cheese dish called Mexican macaroni. Little bottles of Tabasco or packets of cayenne or Mrs. Dash seasoning are included to pep up entrees.

Dried cappuccino and chai are replacing freeze-dried coffee. Powdered Gatorade-type drinks are being tucked into food packs for quick energy. The military has even developed its own power bar, called the HooAH! bar. And some rations contain dried versions of milk shakes in chocolate, strawberry or vanilla.

"You know when you shake this thing up and drink it down, it tastes like you're not here for 15 minutes," one Marine a few miles outside Baghdad told Chronicle reporter John Koopman.

YOUNG SOLDIERS GO FOR IT
Koopman, who ate the old C-rations as a Marine in the 1970s, reports that the new MREs are generally a hit with the young soldiers he's talked to. But, he said, they don't like the fancy stuff.

"What they like most of all is basically beef or meat. Being from San Francisco, I'm the only one who eats the vegetarian meals," he said. "The Marines love me because I'll take the pasta and vegetables."

However, any MRE that has a pack of Skittles or M&Ms is considered a good one, he said. Field studies have shown that young soldiers take comfort in name brands and commercial packaging, so some MREs feature morale-boosting snacks like M&Ms, Lorna Doone cookies, Skittles and Jolly Ranchers, which have become popular currency in poker games.

THE MILITARY'S REQUIREMENTS
The trick, of course, is making all of it work within the military's tight physical and nutritional requirements. The whole package can't weight more than a pound and a half, although the military brass would like them lighter -- and it can't be much larger than a hardback novel.

The food inside the tan plastic MRE bag must be edible for up to three years stored at 80 degrees. The packages have to be waterproof, vermin-proof and able to survive a 100-foot drop without a parachute.

Soldiers heat the food in the field. In the new version, cooking is done by an ingenious chemical heating sheet in a plastic pouch, which soldiers activate by simply pouring in an ounce of water.

Then there are the nutritional demands, as outlined in the eight-page Nutritional Standards for Operational Ratios (NSOR). That job falls to dietitian Judy Aylward at the Natick center. She has to ensure that each meal contains about 1,250 calories, with enough carbohydrate, fat, protein and vitamins to satisfy the surgeon general. That gives each soldier about 3,750 calories a day -- nearly twice the 2,000 calories most of us should eat to stay fit.

FAT 35% OF THE CALORIES
To cram so many calories in such a small space, Aylward has to be creative. Fat accounts for about 35 percent of the calories in each entree, five percent more than most nutritionists recommend. "There's just no way I can get the calories in the package without that fat content," she said.

Sugary drink mixes, jam and candy help pump up the carbohydrate and calorie count. To meet the micronutrient requirements, many of the grain-based items are fortified with vitamins. And because there are more women eating the meals than ever before, folic acid and iron are added.

In the vegetarian meals, getting enough protein and zinc is a problem, so Aylward makes sure those meals have packets of peanut butter. In fact, she is using so much peanut butter, soldiers are complaining.

"No one can eat that much peanut butter," wrote one soldier in a feedback form that hit Aylward's desk recently. "I suggest replacing it with more jalapeno cheese spread, which is excellent."

TWEAKING THE MENU
The crew at Natick constantly tinkers with the MRE menu. Behavioral scientists go through soldiers' trash during field exercises to see what is being thrown out, and study which items get traded or used in unexpected ways, like the cocoa powder and nondairy creamer that soldiers mix into crumbled crackers or pound cake to create "Ranger pudding."

Panels of soldiers and officers evaluate existing dishes and suggest which ones to eliminate. Next year, the Jamaican pork chop and the beef with mushrooms will be out, but New England clam chowder will be in. By 2005, the dreaded Country Captain chicken and Thai chicken will make way for a cheese omelet and chicken fajitas -- the latter a dish that couldn't be included until the commercial producers who contract with the military could wade through the specifications and find a way to keep flour tortillas fresh for three years.

"But they really want pizza and beer," Aylward said. "We're working on it -- the pizza, at least."

E-mail John Koopman at jkoopman@sfchronicle.com.

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