What hormone shifts the body toward fat storage, and what behaviors keep it chronically elevated?
The Short Answer
Insulin is the hormone that shifts the body toward fat storage. When insulin is elevated, your body prioritizes storing incoming energy and restrains the release of existing fat. The behaviors that keep insulin chronically elevated are: eating frequently (snacking), eating refined carbohydrates and sugars, and never allowing enough time between eating occasions for insulin to fall.
Something to Sit With
How many times per day does your insulin spike? Count every eating and drinking occasion that involves calories.
Is your body ever getting enough low-insulin time to access your stored energy?
Learn More
How Insulin Controls Fat Storage.
Insulin is fundamentally a storage hormone. Its job is to manage energy after eating:
When insulin is high:
- Glucose is pushed into cells for immediate use or storage
- Excess glucose is converted to fat (lipogenesis)
- Existing fat stores are locked: lipolysis (fat breakdown) is inhibited
- The body uses glucose for fuel, not fat
When insulin is low:
- The body shifts to burning stored fat for fuel
- Lipolysis releases fatty acids from adipose tissue
- Ketone production may begin
- Stored energy becomes accessible
These states are functionally opposite. You cannot be efficiently storing fat and burning fat at the same time.[1] Insulin is the switch.
What Keeps Insulin Elevated.
Frequent eating. Every eating occasion triggers insulin release.[2] If you eat breakfast, snack, lunch, snack, dinner, snack, that’s six insulin spikes per day. The post-absorptive phase, which Fung places somewhere between six and twenty-four hours after eating, is never reached.
Research by Kishimoto on subclinical reactive hypoglycemia proposes how this could become a vicious cycle: eating spikes insulin, insulin drives blood sugar down, low blood sugar triggers hunger, hunger drives more eating, more eating spikes insulin again. The measured part is narrower: given a 75-gram glucose load, about half of overweight and obese men showed the dip, and those who did snacked six times as often.[3] On that account, snacking begets snacking.
Refined carbohydrates. As discussed in Refined Grains, a food’s glycemic response is not predicted by whether it is a “sugar” or a “starch”: sugar content did not predict it at all. White bread sits at least as high as table sugar. A diet built on bread, pasta, cereals, and crackers keeps insulin stimulated whether or not it contains anything sweet.
Sugar and sweetened beverages. Sugar triggers insulin directly. Liquid sugar (soda, juice, sweetened coffee drinks) is particularly problematic because it absorbs rapidly with no fiber to slow it down.
Large meals. Bigger meals require bigger insulin responses to manage the glucose load. Combined with frequent eating, this maximizes insulin exposure.
Eating late. Research suggests that eating patterns which reduce nighttime eating and prolong the nightly fast may produce sustained health improvements.[4] Eating earlier extends your overnight fast.
The Chronic Elevation Problem.
The issue isn’t that insulin exists or that it spikes after meals. That’s normal physiology. The problem is when insulin never gets low enough for long enough.
On the carbohydrate-insulin model, chronically elevated insulin leads to:
Insulin resistance. Cells become less responsive to insulin’s signal, requiring ever-higher levels to achieve the same effect. Hyperinsulinemia may be primary here rather than secondary (cause rather than consequence), and that “may” is the source’s own.[2]
Weight gain first, overeating second: proposed rather than shown. The carbohydrate-insulin model holds that chronically high insulin drives fat storage, and that overeating follows weight gain rather than causing it. Its underlying physiology is not disputed; whether elevated insulin is the primary cause of human weight gain is, and its own proponents call that evidence inconclusive.[1] Read this section as the model’s account.
Inability to access fat stores. On the model’s account, you might have tens of thousands of calories of stored body fat, but if insulin is high, you can’t access them efficiently, and your body acts as if it’s starving while sitting on abundant reserves.
Hunger despite adequate stores. One review, by Robert Lustig, proposes that overeating and reduced activity may be consequences of weight gain driven by hormones rather than its cause. That is his argument, not an established finding.[5]
How to Let Insulin Fall.
Eat less frequently. Three meals with no snacking gives insulin time to fall between meals. Two meals gives even more time. Extended fasting provides the longest insulin-low periods.
Reduce refined carbohydrates. A meal of protein, fat, and vegetables produces a much smaller insulin response than a meal dominated by refined grains.
Stop eating earlier. Finishing dinner by 7pm and not eating until breakfast (or later) provides a natural overnight fast. Extending this, eating in a smaller window, maximizes time with low insulin.
Eliminate liquid calories. Liquid calories are the ones your appetite tends not to count: solid-food calories draw near-exact compensation at later meals (118%), liquid ones draw none (-17%; fifteen people, soda against jelly beans).[6]
The Unlocking.
When insulin falls and stays low for sufficient time, the body switches modes. You begin accessing stored fat for fuel. Energy becomes stable (you’re running on your reserves, which are abundant). Hunger often decreases (you’re getting fuel, just not from food).
This is what breaking out of fat-storage mode is described as feeling like. The claim underneath it, Lustig’s, is that the lever is hormonal rather than moral.[5]
Further reading:
- Ludwig DS & Ebbeling CB, “The Carbohydrate-Insulin Model of Obesity: Beyond ‘Calories In, Calories Out’”[7] — JAMA Internal Medicine, 2018
- Fung J, The Obesity Code[8] (2016) — Chapter on insulin and fat storage
- Kishimoto I, “Subclinical reactive hypoglycemia with low glucose effectiveness — why we cannot stop snacking despite gaining weight”[9] — Metabolites, 2023
- Rodin J, “Insulin levels, hunger, and food intake: an example of feedback loops in body weight regulation”[10] — Health Psychology, 1985
Written by AI, directed and approved by me. How this is made →