Posted by Werner Mansfeld
on June 24, 2026
For most of the last several decades, “low-fat” was treated as nearly synonymous with “healthy.” Shelves filled with reduced-fat products, and dietary fat carried the blame for weight gain and heart disease. The insulin-resistance research tells a more specific story, and it points in a very different direction than the low-fat era assumed.
What Actually Raises Insulin Levels
Insulin’s primary job is managing blood glucose. Of the three macronutrients — carbohydrates, protein, and fat — carbohydrates raise insulin levels the most, by a wide margin. Protein raises insulin moderately. Fat, on its own, raises insulin minimally, if at all.
This matters because insulin is the hormone most directly responsible for triggering fat storage and, when chronically elevated, driving insulin resistance. A macronutrient that doesn’t meaningfully raise insulin is, by definition, not a primary driver of the mechanism behind diabesity — regardless of its calorie density.
A macronutrient that doesn’t meaningfully raise insulin is, by definition, not a primary driver of the mechanism behind diabesity — regardless of its calorie density.
Why Fat Got Blamed Anyway
Fat contains more calories per gram than carbohydrates — 9 calories per gram versus 4 — which made it an easy target during an era when nutrition science was largely focused on total calorie balance rather than hormonal response to specific macronutrients. The logic seemed straightforward: fewer calories per gram from fat should mean less weight gain.
What that framework missed is that not all calories produce the same physiological response. A diet that reduced fat often replaced those calories with refined carbohydrates — exactly the macronutrient most likely to spike insulin and drive the fat-storage mechanism. The low-fat era may have inadvertently increased insulin resistance for a large segment of the population by encouraging exactly the substitution that makes the underlying problem worse.
What Healthy Fat Actually Does
Beyond simply not spiking insulin, dietary fat offers several specific advantages relevant to insulin resistance and weight management:
- It promotes satiety, helping people feel full on fewer total calories without intentional restriction
- It improves the flavor and palatability of food, which supports long-term adherence compared to diets that feel restrictive
- It serves as a stable, steady energy source that doesn’t trigger the spike-and-crash pattern associated with high-carbohydrate meals
Why This Doesn’t Mean Unlimited Fat
This isn’t a case for eating unlimited quantities of any fat source. The type and quality of fat matters — healthy fats from sources like olive oil, avocado, butter, and fatty fish behave very differently in the body than industrially processed seed oils, which carry their own separate risks related to oxidation and inflammation. The argument here is specifically about fat as a macronutrient category relative to carbohydrates and their effect on insulin — not a blanket endorsement of every fat source regardless of quality.
The Bottom Line
If your goal is managing insulin resistance, the relevant question isn’t “how many calories” in isolation — it’s which macronutrient is actually driving the insulin response that drives fat storage.
The bottom line
On that specific question, the evidence points toward carbohydrates as the primary lever, with healthy fat serving as a tool that supports the goal rather than working against it.
