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Short Summary
Main recommendation: Do not switch away from a ketogenic diet, or use carb cycling or cyclic keto to "prevent insulin resistance," because Dr. Benjamin Bikman says the premise is wrong; fasting and keto cause a temporary loss of the first phase of insulin secretion, not insulin resistance. He explains that the body is highly insulin sensitive, and that the effect reverses quickly once carbohydrates return.
Key Points
- The effect commonly called "insulin resistance" from fasting or keto is actually a glucose-sparing effect, which Bikman says is more accurately described as a temporary loss of first-phase insulin secretion.
- Eating a starchy or sugary meal normally triggers two insulin release phases: a rapid first bump from preformed insulin stored in beta cells, then a larger second bump from newly made insulin.
- Human evidence cited by Bikman shows that even a roughly 16-hour fast can reduce or nearly blunt that first phase.
- Glucose rises higher and stays higher after a glucose load in people on keto or fasting, which can look like insulin resistance but is a different mechanism.
- Bikman states that the body is "exquisitely" insulin sensitive, citing George Cahill's decades-old findings that insulin injection rapidly drops glucose in fasting or keto subjects.
Details Worth Noting
- Concrete instructions:
- If you are on keto or fasting and must take an oral glucose tolerance test, eat some carbohydrates in the one or two days before the test to "prime the pump," because the beta cells will then have preformed insulin ready to release.
- Do not adopt carb cycling or cyclic keto specifically to keep your body insulin sensitive, since Bikman says that reason is false; he says carb cycling is "fine" and "might have a place" for other reasons.
- Bikman says the loss of first-phase insulin is acute and quickly reversible, so he considers it not a permanent concern.
- He noted that his team is running rodent studies to confirm the ketogenic diet effect; human data so far concerns fasting, and the 16-hour fast study is the example he cited.
- He described the claim as "BS" and said the term is misused in popular discussion, though he welcomes attention to insulin resistance generally.
Bottom Line
The main worry about keto or fasting harming insulin sensitivity is, according to Bikman, a misunderstanding of a short-lived change in insulin release timing, so it does not justify switching diets to avoid it.
