You do a fast of a few days. No red meat, no beer, nothing. And yet your blood work shows uric acid higher than usual. Makes no sense? It actually does. The problem isn't what you eat. It's what your body makes when you don't eat.
We've known this since the '60s
This isn't new. In 1965, a researcher named Cheifetz noticed that in women on a prolonged fast, the kidneys cleared less and less uric acid as ketone levels rose in the blood. And when ketones were infused directly, the same thing happened.
In 1976, a research team (Fox and colleagues) followed 15 people through a medically supervised 28-day fast. Their uric acid went from an average of 5.9 to 12.5 mg/dL in one week. More than double. Then, interestingly, it came back down to around 7.7 mg/dL by the end of the fast, even though ketones stayed high.
Even earlier, in 1967, two physicians (MacLachlan and Rodnan) saw uric acid climb as early as the first or second day of fasting. Among nine patients who already had gout, eight had at least one flare during those rapid swings.
The culprit: busy kidneys
When you fast, your liver makes ketones to feed your brain and muscles. Those ketones leave the body through the kidneys, using the same exit routes as uric acid. So they take up the space, and uric acid builds up in the blood. Your plate has nothing to do with it. When you're fasting, it's empty anyway.
What about intermittent fasting?
This is where we have to be honest: almost all of this data comes from multi-day fasts, not a daily 16:8 window. There's no solid study yet that measures uric acid on 16:8.
The few modern data points suggest a fairly modest effect. In a 2026 trial on alternate-day fasting (35 adults with obesity, followed for 62 days), uric acid rose about 9% during the strictest restriction phase, then dropped about 7% in the next phase. Another 2026 study, in 43 postmenopausal women over 6 months, found that intermittent fasting had no significant effect on uric acid. Only a very-low-calorie ketogenic diet brought it down. These are small studies, so we stay cautious in both directions.
In practice
If you've ever had gout, talk to your doctor before trying fasts that last several days. That's the setting where flares were documented. Drink enough during your fasting window. And if a blood test shows slightly high uric acid during a fasting stretch, mention it: that context completely changes how the number should be read.
We started Fasted Rebels to talk about fasting as it really is, with what we know and what we don't. Feed the mission. Not the hunger.
This article is for information only and isn't a substitute for advice from a health professional.
Sources: Cheifetz PN, "Uric acid excretion and ketosis in fasting," Metabolism, 1965; MacLachlan MJ, Rodnan GP, "Effects of food, fast and alcohol on serum uric acid and acute attacks of gout," American Journal of Medicine, 1967; Fox IH, Halperin ML, Goldstein MB, Marliss EB, "Renal excretion of uric acid during prolonged fasting," Metabolism, 1976; Li Y et al., modified alternate-day fasting trial, Frontiers in Nutrition, 2026; Pala B et al., "Serum Uric Acid as a Cardiovascular Risk Marker: Differential Effects of Ketogenic Diet and Intermittent Fasting in Postmenopausal Women," Nutrients, 2026.
French version: Pourquoi ton acide urique grimpe en plein jeûne
Also read, the fasting and electrolytes series: Why You're Cramping Mid-Fast · More Water While Fasted Isn't Always Safer · Why You Get Dizzy Standing Up Mid-Fast · Why Your Heart Pounds Mid-Fast · Why You Twitch and Sleep Like Garbage Mid-Fast · Why You Get a Headache Mid-Fast · Why You're Always Cold Mid-Fast · Why Your Creatinine Spikes on a Blood Test · Do You Need Sugar to Get Creatine Into Your Muscles?