An analysis of Americans’ diets from 1970 to 2010 reveals we have a way to go in cutting down on harmful fats and starches to ward off obesity, diabetes and heart disease.

From time to time, the Center for Science in the Public Interest, a Washington-based advocacy group, prepares an updated “report card” on changes in the American diet. The latest, collated by the nutritionist Bonnie Liebman and published in the September issue of the center’s Nutrition Action Newsletter, is not one Americans should be especially proud of.

The analysis of changes in food consumption from 1970 to 2010 reveals that we still have a long way to go before we come close to meeting dietary guidelines for warding off obesity and chronic health problems like diabetes and heart disease.

The news isn’t all bad. Our consumption of added sweeteners, though still significantly higher than it was in 1970, has come down from the “sugar high” of 1999 when the average was 89 pounds per person. Nonetheless, an average of 78 pounds per person in 2010, mostly as sugar and high-fructose corn syrup, is still too much, Liebman points out.

Even our B-plus for cutting back on fats and oils, the highest grade Liebman awarded, is a mixed bag. Yes, we’ve dramatically reduced consumption of heart-damaging trans fats and, to a lesser extent, saturated solid fats like margarine and shortening. But there’s been a steady, steep climb in total fats added to the diet in the form of salad oils and cooking oils.

As a country, we have definitely not been on a “low-fat diet.” The average person consumes 20 pounds more in total fat yearly than in 1970, which partly explains why the obesity rate among adults has more than doubled since then, when only 15 percent of Americans were obese.

In 2005, the Agriculture Department has reported, the average American consumed 645 calories a day in added fats and oils, not counting the fats naturally present in foods like meats and dairy products.

Americans seem to think that if a food is considered a healthier alternative, it’s OK to swallow as much of it as one might like. People forget, or never knew, that a tablespoon of olive oil or canola oil has about the same number of calories as a tablespoon of lard (about 115), and even more calories than a tablespoon of butter or margarine.

“We never were on a low-fat diet,” Liebman said in an interview. “We increased our fat intake from pizzas, burgers, french fries, baked goods and restaurant-prepared foods.”

Likewise, grain products. “There’s been a huge increase in grains in the last 30 years — bread, cereal, pasta, rice, burritos, pizza crust, panini, muffins, scones — mostly made from white flour,” she said. “We’ve been blaming the obesity epidemic on sweets, and we are eating too much sugar, but we need to pay more attention to grains.

“It would not be great to simply replace refined grains like white flour and white rice with whole grains,” she added. “We need to cut back on grains, period.”

Whether made from white flour or whole wheat, one unadorned New York-style bagel supplies about 500 calories, and a 21st century muffin often contains as many as 800 calories.

For the average adult, who should aim for a daily intake of 2,000 calories, these grain foods displace far more nutritious (and relatively low-calorie) fruits and vegetables. Our consumption of those earned a B-minus on Liebman’s report card.

“We need to replace sandwiches with salads, swap starches for veggies and trade cookies, cupcakes and chips for fresh fruit,” she wrote.

Liebman was surprised to find that combined consumption of beef and pork is still higher than that of chicken and fish. Although chicken itself is now slightly more popular than beef, our consumption of fish has remained relatively flat.

In the July/August edition of the Nutrition Action Newsletter, Barton Seaver, the director of the Healthy and Sustainable Food Program at the Harvard School of Public Health, noted that Americans “eat only about 16 pounds of seafood per person per year, and about 95 percent of that comes from only 10 species.”

Seaver, a former chef, encourages diners to stray from the familiar to more sustainable — and wholesome — species like pollock, sablefish, Spanish mackerel, haddock, and farm-raised barramundi and shrimp. He champions farm-raised mussels, clams and oysters as sources of “fabulous” lean protein that clean the aquatic environment.