Fasting-Mimicking Diet (FMD).

The commercial version (ProLon) provides pre-packaged meals for 5 days: soups, bars, crackers, olives, supplements, and herbal teas, all calibrated for specific macronutrient ratios — high fat, low protein, low carbohydrate — designed to maintain fasting-like metabolic signaling while providing essential micronutrients. Day one provides roughly 1,100 calories; days two through five provide roughly 750 calories each. The protocol is repeated every 1 to 6 months depending on the individual's health goals and biomarkers.

The FMD has been studied in multiple randomized controlled trials. Published results include reductions in body weight, trunk fat, blood pressure, fasting glucose, IGF-1, and C-reactive protein after three monthly cycles. The effects are most pronounced in participants who started with elevated metabolic risk markers. For healthy participants with normal baseline markers, the changes are more modest. The clinical data is more robust than for any other modified fasting protocol, which is the primary reason it receives attention.

The FMD was designed to capture the metabolic benefits of prolonged fasting while reducing the risks and improving adherence. Compared to a 5-day water fast, the FMD provides enough nutrition to avoid the most dangerous complications (severe electrolyte depletion, refeeding syndrome), allows people to continue daily activities, and has a published safety profile. The trade-off is that the metabolic depth of the fast is less than a full water fast — autophagy markers, for example, are likely lower — but the safety profile is substantially better.

The commercial ProLon kit costs $150 to $250 per 5-day cycle, depending on the retailer and subscription model. This is expensive relative to simply not eating, which is why some people attempt DIY versions using the published macronutrient ratios. The DIY approach loses the specific formulation and the clinical data behind it — the published trials used the commercial kit, and there is no data on DIY approximations. Whether the premium is worth the clinical specificity is a personal decision.

Adults with elevated metabolic risk markers who want the benefits of periodic fasting without the risks of full water fasting. Adults over 50 pursuing longevity strategies. Adults who have tried and failed to maintain longer fasting protocols. The FMD is not designed for weight loss as a primary goal — it produces modest weight loss, but caloric restriction over 5 days is not an efficient weight loss strategy. It is designed for metabolic and cellular health optimization.

Are you using the commercial ProLon kit or a DIY approximation? How many cycles have you completed, and are you tracking biomarkers between cycles? Have you discussed this protocol with your physician, particularly if you are on any medications? What are your specific health goals — metabolic optimization, longevity markers, or weight loss — and is the FMD the right tool for those goals?