Body Language : Moody? Depressed? Tired? Translation: You could be getting the word that your diet is all wrong.

When the death of a business associate threw Frank Nemiroff’s restaurant supply company into turmoil, Nemiroff expected the rough road that followed--the chaos of moving and reorganizing his business and the 14-hour workdays.

It was the constant hunger and lightheadedness that took him by surprise.

“I couldn’t concentrate, and I had trouble working with numbers,” recalls Nemiroff, 34, of Venice. “People would talk to me, but their words wouldn’t find their way into my brain. I’d find myself getting a little irritable. I’d have less patience with myself and others, and I’d withdraw.”

As it turned out, the culprit wasn’t stress, although stress probably triggered the problems. It was Nemiroff’s diet.

Unlike many anxiety-ridden people, Nemiroff wasn’t scarfing down truckloads of Oreos; he actually stuck to his usual high-carbohydrate, low-fat way of eating. But that wasn’t working. On the advice of his wife, a nutritionist, Nemiroff cut down on carbohydrates and stocked up on protein.

“Instead of bagels and cereal, I began to eat canned tuna, smoked salmon, roasted turkey and cottage cheese,” he says. “Almost immediately, I had more energy. I was able to complete projects without having to take food breaks. I wasn’t dozing off, and my patience improved.”

What, so now protein’s in and carbs are out? No, experts say, it’s not another diet fad. The real point of Nemiroff’s experience is something scientists and nutritionists are just now discovering: “More often than not, even minor changes in what and when you eat can have pretty astounding effects on how you feel,” says Elizabeth Somer, a Salem, Ore., nutritionist and author of “Food and Mood” (Henry Holt, 1995).

The food choices you make, experts say, often can determine whether you’re grouchy, happy, depressed, alert, calm or sleepy. They can help you rise to the occasion under stress, or lead you to conk out at your desk. They can even determine how moody a woman gets before her period.

What you ate for breakfast could mean the difference between putting a curse on employees at the Department of Motor Vehicles and saying, “Gee, it’s fun to stand in line at the DMV.”

The key, experts say, is to figure out which foods work for your body, and to understand how your food choices affect how you feel. For some people, specific foods can trigger certain moods. Some people are so sensitive to sugar, for instance, that even one glazed doughnut can send them on a mood-swing roller coaster.

Larry Christensen, chairman of the psychology department at the University of South Alabama, has tested more than 100 clinically depressed subjects and found that, for at least 30% of them, depression vanishes--within a week--when they eliminate sugar. For others, caffeine is the offender.

“With these sensitive people, I can turn depression on and off like a water faucet,” Christensen says.

Science can’t yet explain why sugar has such a dramatic effect on some people, but Christensen recommends that they eliminate all added sugar, including foods that contain hidden sugars, such as ketchup, fruit drinks and fruit yogurt.

For other people, like Nemiroff, too much carbohydrates--not just added sugar, but starch as well--can lead to lethargy and irritability. They don’t metabolize carbohydrates in an effective way, says Santa Monica registered dietitian Bonnie Modugno; their body’s cells don’t get enough nourishment, in the form of glucose, from the bloodstream.

“They complain that they can’t concentrate, and they can’t think clearly,” Modugno says. They tend to get immediate satisfaction from eating more carbohydrates, but that may only exacerbate the situation in the long run. These people may be better off eating less carbohydrates and more protein, whether it’s meat, dairy products, tofu or beans.

For many people, mood swings are caused not by specific foods, but rather by a shortage of calories, vitamins and minerals. “People don’t realize that malnutrition is a major cause of depression,” Modugno says. “When people restrict their caloric intake, it has a phenomenal behavioral impact.”

Problems include depression, excessive sleeping and impatience. “Our tolerance goes right through the window,” Modugno says. It’s a subtle form of malnutrition that’s especially pervasive in Los Angeles, where fat is considered evil, she says. And it’s a particular problem among women. “They think they’re doing this healthy thing--they don’t put butter on their potato, they eat only three ounces of meat, they only eat fruit for snacks, they have a cup of cereal for breakfast. They cut out eggs, cheese and red meat, and they eat fat-free this and fat-free that. They have this restrained eating mind-set.”

This is a problem because our emotions, thoughts and behavior are orchestrated in large part by our neurotransmitters--the chemicals that transmit messages between nerve cells, and between nerve cells and the rest of the body. Many neurotransmitters are made up of amino acids, which are obtained from the diet.

When you don’t consume enough of certain amino acids, your body limits production of the neurotransmitters, and you experience mood changes. Also, eating too much of a particular nutrient, such as fat or carbohydrate, can trigger neurotransmitter imbalances.

It’s not just the energy nutrients (carbohydrate, protein and fat) that can affect your mood. Vitamins and minerals also play a role because many of them--such as Vitamin B1, folic acid, Vitamin C and magnesium--either help make neurotransmitters or protect them from damage. A mineral deficiency, even a subtle one, can cause mood changes. If you’re short on iron, for instance, less oxygen will make it to your tissues and brain; you’ll feel tired and irritable, and you may have trouble concentrating. Even a marginal magnesium deficiency can result in confusion, personality changes and stress-related depression, Somer says.

Another food-related cause of moodiness is skipping meals. “It’s one of the worst things we can do,” says Deborah Waterhouse, a registered dietitian from Montclair and author of “Why Women Need Chocolate” (Hyperion, 1995). “Your blood-sugar level drops and your brain protests, and you kind of feel like an alien being all of a sudden. It’s your body’s way of saying you made a mistake.”

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At no time is it more important to eat well than when you’re under stress.

“Stress can severely impact the way the body handles nutrient intake,” Waterhouse says. When you’re filled with anxiety, she says, your brain becomes even more sensitive to changes in blood-sugar levels. Stress also increases your need for carbohydrates, protein and calories as well as several vitamins and minerals, including antioxidants, B vitamins and iron. At the same time, anxiety and tension decrease your body’s ability to absorb these nutrients.

In one study, researchers at the U.S. Department of Agriculture burdened employees with extra work and impossible deadlines for five days; they found the subjects’ blood levels of several minerals dropped by as much as 33%--even though the subjects ate adequate diets.

That’s probably what happened to Nemiroff when he relocated his business. Although he ate plenty of healthy foods and about 4,000 calories a day, he says, “I felt like I was always hungry.” Although he still has plenty of job stress, he says that changing his eating habits has helped him cope.

Eating the right foods can not only help you deal with stress, experts say, but it also can reduce mood swings in women with premenstrual syndrome.

Somer says sugar sensitivity might be aggravated during PMS, intensifying the emotional highs and lows. She points to a study conducted at MIT, which found that PMS sufferers were less tense, angry and tired when they ate a bowl of corn flakes rather than a candy bar. Women who drink tons of caffeine are more likely to have PMS than are women who consume less caffeine or none at all, research shows. In addition, PMS sufferers consume more calories but fewer vitamins and minerals than do other women.

“They go to all the wrong foods,” Somer says. “They double their sugar intake, but what they end up doing is making the matter worse. The irritability worsens, and then they go back to the foods that are amplifying the condition.”

Nutritionists emphasize that there’s no single diet that can keep everyone from becoming Oscar the Grouch.

“Think of your body as the expert in directing you,” Waterhouse says. “Respond to your body’s signals.”

‘People don’t realize that malnutrition is a major cause of depression. When people restrict their caloric intake, it has a phenomenal behavioral impact.’

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Improve Your Mood Through Food

If you suspect your food choices are turning you into Sleepy, Grumpy or Dopey, don’t attempt to become Happy overnight.

Here’s a list of ways you can use food to improve how you feel mentally and physically:

* Eat breakfast and include protein. If people don’t eat a satisfying breakfast, says Santa Monica registered dietitian Bonnie Modugno, “They run down to the candy machine and eat crap all day. Then they start feeling hungry, and they get less and less productive.”

* Eat four to six small meals evenly throughout the day to keep your blood sugar levels stable. A dip in blood sugar can cause irritability and fatigue. “The brain thinks it’s in a state of emergency, and demands, ‘Give me sugar right this very minute,’ ” says registered dietitian Deborah Waterhouse, author of “Why Women Need Chocolate” (Hyperion, 1995).

* Limit caffeine. A cup of coffee can give you an instant charge, but it can leave you crabby a few hours later.

* Cut down on sugar. Eliminating added sugar can cure depression in some people.

* Take a vitamin/mineral supplement. Most Americans don’t even consume adequate--let alone optimal--amounts of vitamins and minerals. Even marginal deficiencies can wreak havoc on your mood. Consider a supplement especially if you consume fewer than 2,500 calories per day or are under stress.