(CNN) -- "To eat, or not to eat?" For many people these days, that really is the question.
For the past four decades, we've been told to stay away from red meat, dairy and cheese -- foods high in saturated fats -- because saturated fat is bad for the heart.
But investigative reporter Nina Teicholz says that isn't the case.
"When the dietary recommendations came out in 1961 saying that saturated fat causes heart disease, that was based on total cholesterol," Teicholz said. "But our understanding of heart disease has evolved enormously."
She said the science condemning saturated fats just isn't there. In her new book, "The Big Fat Surprise," Teicholz writes that the low-fat, fruit- and vegetable-filled diet that you thought was healthy doesn't have all the benefits it claims.
Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health, cautions readers to take her findings with a grain of -- well, not salt.
Your risk for heart disease depends on HDL and LDL cholesterol: good and bad cholesterol. And scientists know, he said, that saturated fat raises unhealthy LDL levels in the blood.
Willet said the science is there to show saturated fats are not healthy. Sure, if you compare saturated fats to everything else in a person's diet, they may not look very damaging, especially compared to say, sugar.
But the idea that saturated fats are not all that bad is "only sort of a half a truth," Willet said.
The keys to heart disease
"Saturated fat has been the dietary culprit of the past 50, 60 years, " said Teicholz. "It really goes back to the 1950s when America was in the throes of the heart disease epidemic, which had risen out of nowhere to become the nation's No. 1 killer. President Eisenhower himself had a heart attack in 1955."
It was at this time that Dr. Ancel Keys, a scientist at the University of Minnesota, embarked on the landmark "Seven Countries" study that examined the correlation between cholesterol and heart disease in nearly 13,000 men. What Keys found would become the basis for the nutritional guidelines that we have today: that countries with diets high in saturated fats had higher rates of heart disease.
"There were other ideas at the time, but Ancel Keys got that idea and planted it into the American Heart Association... and it's like, the rest is really history from there," Teicholz said. "It had never been tested."
But as Tiecholz and other critics point out, Keys cherry-picked the seven countries he visited: the United States, the Netherlands, Finland, Yugoslavia, Italy, Greece and Japan.
Noticeably absent? Countries well known for their rich fatty foods but without high rates of heart disease, like Switzerland, Sweden and West Germany.
Based on his study, Keys promoted the Mediterranean diet: a diet high in fruits and vegetables, along with bread, pasta, olive oil, fish and dairy. But Teicholz pointed out that Keys visited Greece during Lent, a time when people abstain from eating meat, which in turn skewed his data.
In reality, she said, the data to support the low-fat diet just isn't there.
Take the 30-year follow-up to the landmark Framingham Heart Study, for example. It is one of the largest epidemiological studies evaluating the roots of heart disease in our country.
In the follow-up, scientists found that half the people who had heart attacks had below-average cholesterol levels. In fact, scientists concluded that "for each 1% mg/dL drop of cholesterol, there was an 11% increase in coronary and total mortality."
"Cholesterol matters, but not in the way we think it does," said Teicholz. "Our understanding of cholesterol now is very different than it was when we condemned saturated fat."
Willett pointed out that studies have found that replacing saturated fats with healthy fats improves blood lipids, and in turn reduces heart disease. "What matters is what you replace it with," he said.
Too frequently people substitute fats with sugars, often in the form of carbohydrates, Teicholz said. Instead of eating steak for dinner, they have a plate of pasta.
"We've decreased the amount of fat we eat and shifted over," Teicholz said. "In the last 30 years we've decreased our saturated fat consumption by 11%, increased carbohydrates by 25%."
And sugar, some scientists believe, is the main reason for obesity in America, causing everything from hypertension to diabetes.
Dr. Dean Ornish, founder of the Preventive Medicine Research Institute, helped President Bill Clinton get in shape by switching him over to a vegan diet. Ornish said the answer to reducing heart disease isn't more meat.
"If you eat a diet that is high in animal protein, your risk of dying from everything goes up considerably. If you eat a plant-based diet, which is naturally low in fats and refined carbs, a whole foods, plant-based diet," the disease risk decreases, Ornish said.
Perhaps the issue is that our health is a bit more complicated than choosing between a piece of meat or plate of pasta.
As Willet explained, "It's like an orchestra -- you have to have all the pieces there and have to have it in the right balance. Not one factor is going to solve your health issues."