Does the fasting-mimicking diet, such as Prolon, actually work?
The fasting-mimicking diet improves measurable risk factors such as blood sugar, blood lipids and abdominal fat across multiple human studies. Some studies were funded by the manufacturer of ProLon, so independent confirmation carries more weight than those results alone.
Three cycles of 5-day FMD per month reduced body weight, abdominal fat, blood pressure and IGF-1 (a growth factor linked to ageing) in 71 generally healthy adults. The effects were greatest in people who already had elevated values. No serious side effects were reported.
Those same 3 cycles were associated with a reduction in measured biological age of 2.5 years on average, less liver fat and a more favourable immune profile. These are biomarkers, not hard disease outcomes, and two of the researchers involved have a financial interest in L-Nutra, the company behind ProLon. That warrants caution regarding those specific findings.
An independent British study tested two variants of an FMD providing approximately 850 kcal per day in healthy adults. Both versions improved glucose (around 10%) and IGF-1 (a growth factor linked to ageing, around 35%). A high-protein variant produced additional benefits for abdominal fat, blood lipids and heart rate variability. This suggests that the precise composition matters, and that ProLon's low-protein formula is not necessarily the optimal choice.
In people with overweight or obesity, 6 FMD cycles also improved smell and taste function alongside cardiometabolic markers, and some patients with diabetes were able to reduce their medication use. If you have diabetes and are considering this, discuss it with your doctor first, as medication adjustments require medical supervision.
The most striking result comes from cancer research. In the Dutch DIRECT trial involving 131 breast cancer patients, FMD administered around chemotherapy cycles led to better tumour response and less DNA damage in immune cells, without additional side effects. An Italian study in 101 cancer patients confirmed that FMD can be safely combined with standard treatments. These are encouraging results, but larger confirmatory studies are still needed. FMD in the context of cancer must only be used under medical supervision.
The evidence is based on multiple studies in humans, including several randomised trials. The findings on body weight, blood glucose and blood lipids are supported by independent research. The biological ageing finding (2.5 years less biological age) comes from a secondary analysis in which two researchers have a financial interest in the company that makes ProLon; that finding warrants additional caution. The cancer studies are encouraging but are still phase 2: they are not large enough to make definitive statements about survival.
Does a fasting-mimicking diet work better than simply eating less?
A fasting-mimicking diet has promising effects on several health markers, but whether it works better than simply eating less has not yet been demonstrated. If you want to try it, be aware that independent long-term data are still lacking and that the costs of commercial packages are a real consideration.
Can you drink coffee during intermittent fasting?
Black coffee fits comfortably within intermittent fasting and is explicitly listed as a fasting drink in dietary guidelines. If you add a significant amount of milk or sugar, you break the fasting window.
Which form of intermittent fasting works best?
Alternate-day fasting has the strongest short-term evidence for weight loss, but the advantage over simply eating less is small and disappears after six months. Which approach suits you best depends on what you can sustain the longest.
Can you drink coffee with milk while fasting?
Milk in coffee breaks your fast: it stimulates insulin release and counts as food intake. If you want to keep your fasting period intact, drink your coffee black.
Does extra protein help with losing weight without losing muscle?
Extra protein helps preserve muscle mass while losing weight, but works best in combination with strength training. Aim for 1.2 to 1.6 grams per kilogram of body weight per day if you are not an elite athlete, or 1.6 to 2.4 grams if you are, and always combine it with training.
Does the 16:8 schedule work better than other forms of intermittent fasting?
16:8 works better than shorter fasting windows in the short term, but over the long term it is not demonstrably better than simply eating fewer calories. Choose the approach you can sustain best.