'Eating fat makes you fat' idea debunked: dietitian

The science surrounding a low-fat diet has changed, but our attitudes haven’t kept up, a dietitian says.

Healthy fats have been replaced in prepared foods with sugar and salt to add flavour

Sometimes we eat more of low-fat foods thinking that they're guilt free and we end up eating more calories, says dietitian Russell de Souza. (CBC)

The science surrounding a low-fat diet has changed but our attitudes haven't kept up, a dietitian says.

The idea that saturated fats were associated with high cholesterol and heart disease was sparked by the Seven Countries Study of middle-aged men in Greece, Italy, Spain, South Africa, Japan, Finland and the U.S.

Based on the findings of the 1950s study, Minnesota physician Ancel Keys warned about the risks of fatty foods.

The idiom "eating more fat makes you fat" was engrained in the 1970s but it hasn't survived the test of time, says  Russell de Souza, a registered dietitian and professor of nutritional epidemiology at McMaster University in Hamilton, Ont.

It might be best to opt for a small amount of regular chips instead of a larger amount of a low-fat variety. (Matthew Mead/Associated Press)

"Fat is not the enemy," de Souza said. "What's more important than the amount of fat we consume is the type of fat we consume."

Now the advice includes:

  • Avoid harmful artificial trans fats, used to hydrogenate vegetable oils into a solid such as those used in shortening, because they raise the risk of heart disease, increase bad cholesterol levels and reduce good cholesterol levels.
  • Choose heart-healthy fats such as monounsaturated fats and polyunsaturated fats from nuts, fish and plant-based vegetable oils.
  • Don't increase saturated fats found in meat, eggs and dairy above about 10 per cent.
  • Focus on the whole diet, not specific nutrients.

Healthy fat replacements

"When the food industry got fat out of the food​ supply, often times what it was replaced with was refined carbohydrates like refined flours and sugars," de Souza said. "We think that from a heart disease perspective, that's really been shown to be a wash. If you take animal fats or total fats out, and you replace it with an ingredient that's just as bad, it's kind of like we went out of the frying pan but into the fire."

Cutting fat from the diet doesn't always lead to wiser choices, de Souza said.

As one example, he compared the labels on low-fat baked potato chips with regular potato chips. The low-fat chips are lower in fat, but also higher in carbohydrates and sugar.

"Sometimes we tend to eat more of low-fat foods thinking that they're guilt free and we end up eating more calories than we wanted from the low-fat foods because they're also not as satisfying and not as satiating," he said.

De Souza suggests eating a small amount of regular chips instead of a larger amount of a low-fat variety.

He also gave the example of comparing labels on low-fat salad dressing vs. regular. The first ingredients on the low-fat version are water, vinegar, salt and sugar, while water and soybean and canola oil top the list in the regular dressing.

"What we've done is we've taken the healthy fats out and we've replaced it with sugar and salt to add flavour," he said.

And the advice to eat more fresh fruits and vegetables still stands.


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