Does fat make you thin?

Last month this article came across my nutrition news feed: Whole Milk Compared With Reduced-Fat Milk and Childhood Overweight. Based on all our preconceived notions about fat, what would you assume the study showed? That reduced-fat milk kept children from being overweight, because Fat is Bad? You’d be wrong.

In fact the study found that kids who drink whole milk were less likely to be fat than kids who drank reduced-fat milk. How can this be? Haven’t we been brainwashed taught for decades about the dangers of consuming fat, especially the saturated fat found in dairy foods?

The article got me thinking — again — about our widespread fear of fat. How did we get here?

It all started back in the mid-20th century. Our understanding of fat was pretty unsophisticated. Fat = calories — 9 calories per gram, more than carbohydrates or protein. The assumption was that fat was just empty calories that go right to your hips. The solution seemed easy: avoid eating fat and you won’t be fat.

At the same time, research claimed that saturated fat caused heart disease. Major health policy organizations sounded the alarm about saturated fat in meat and dairy foods. Our food supply shifted to low fat dairy and lean meats. School lunch programs switched to low fat milk. Years later, we’re dealing with an epidemic of obesity and diseases linked to obesity. Low fat diets haven’t worked as expected.

It turns out the simplistic way of thinking about fat — it’s all just calories — may be seriously flawed. “Fat” is not one homogenous thing. It’s a complex mix of lots of different fatty acids.

Fatty Acids 101

Fatty acids are chains of carbon atoms. Some chains are long (16, 18 or more carbons). Some are short (just 2 or 4 carbons). Some chains have so-called double bonds between the carbons. A chain with no double bond is saturated; a chain with one or more double bonds is unsaturated.

The fatty acid mix is unique to each food. The fat in beef has more longer chain saturated fatty acids. Dairy foods have more shorter chain saturated fatty acids. Plant oils tend to have predominantly unsaturated fatty acids. Coconut fat is an exception; it’s highly saturated. The more unsaturated fatty acids in the mix, the more liquid the fat at room temperature.

Keep in mind, whatever the source, food fats are typically a mix of different fatty acids. This is an important concept when thinking about the whole milk study. Dairy and beef fats may both be mostly saturated, but the fatty acid mix of dairy is distinctly different from beef. Back in the mid-20th century, this difference was considered irrelevant. The assumption was that all fatty acids are metabolized the same. Turns out this is wrong.

You don’t need to understand all the fine points of biochemistry and human metabolism. Suffice it to say, different fatty acids — different lengths and different double bonds — have different impacts on body fat and metabolism. Compared to long chain saturated fats, the short chain versions are metabolized differently and may also impact gut microbes in ways that might be healthful.

Compared to meat, whole milk has more short and medium chain saturated fats. Whole milk, cheese, cream and other high fat dairy foods also have higher levels of these types of fatty acids. This could explain why children drinking whole milk are less prone to being fat. It’s not just about the calories in the milk fat; different fatty acids may have metabolic benefits.

Think about this: why are people in traditionally high dairy consuming cultures — Scandinavia, the Netherlands, etc. — generally thinner? Not to mention France, where high fat cheeses are widely consumed. If dairy fats are so terrible, obesity should be epidemic in those countries. It’s not. Meanwhile ever since fat phobia changed our food supply, obesity has gotten nothing but worse. Maybe our simplistic assumptions about fat in food are all wrong.

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