Eating a lot of saturated fat might make your body less responsive to insulin and cause fat to build up in your liver. If you also eat a lot of protein, it could push your body to make more sugar, which might raise your blood sugar—especially if you're prone to it.
Evidence from Studies
Supporting (2)
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Substituting dietary saturated for monounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU study
The study found that eating more saturated fat made the body worse at using insulin, which matches part of the claim. But it didn’t test high protein or liver fat, so we can’t be sure about those parts.
Out of the frying pan: dietary saturated fat influences nonalcoholic fatty liver disease
The study found that just one dose of saturated fat made the liver store more fat and become less sensitive to insulin, and it increased sugar production in the liver—this supports the idea that saturated fat can harm liver and blood sugar control.
Contradicting (1)
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Diets high in protein or saturated fat do not affect insulin sensitivity or plasma concentrations of lipids and lipoproteins in overweight and obese adults.
The study looked at high fat and high protein diets in overweight people and found they didn’t worsen insulin sensitivity or blood fats. It did see a small rise in fasting blood sugar with more protein, but overall, the results don’t support the idea that these diets harm blood sugar control in most people.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.