McDonald's is bringing an unusually salty offering to Chicago Marathon weekend, handing out bottles of “Pickle Boost” as runners prepare to cover the course. Yet a sports dietitian cautions that scientific evidence supporting pickle juice as a remedy for muscle cramps remains mixed.

The fast food company plans to distribute the limited bottles beginning Oct. 9 and continuing through race day on Oct. 11. Runners, spectators and pickle enthusiasts are all included in the promotion.

McDonald's said the idea draws on the popularity of pickle juice among athletes, some of whom reach for the briny drink when muscle cramps develop during exercise. The promotion places that familiar practice directly along the marathon route.

Bottles will first be offered during a Friday morning pop up on Chicago's Lakefront Trail. On race day, participants can also find them at five McDonald's restaurants located along or near the route, while supplies last.

The belief that pickle juice can prevent or relieve cramps has circulated among athletes for years, and some research offers limited support. However, the available findings do not provide a clear answer about whether the drink reliably works.

“Pickle juice may help relieve muscle cramps, but the research is mixed,” said Jena Brown, RD, CSSD, a sports dietitian in Texas and owner of Victorem Performance Nutrition. Her practice works with endurance athletes, and Brown is also a longtime runner.

Brown cited one small study in which pickle juice appeared to help electrically induced cramps subside faster than water among dehydrated participants. That study did not examine runners competing in an actual marathon, while another study found no benefit.

The uncertainty reflects a broader question surrounding exercise related cramps. “Muscle cramps are not fully understood and are likely not induced by a singular cause for all runners,” Brown said.

Losses of electrolytes may contribute to cramping for some athletes, but Brown said any potential effect from pickle juice might involve more than sodium replacement. One theory proposes that vinegar stimulates receptors in the mouth and gut, affecting communication between the nervous system and muscles.

Evidence supporting that explanation remains limited. Brown said runners should not treat pickle brine as the central component of their strategy for completing the race.

“Pickle brine is not a replacement for a hydration and fueling plan ,” Brown said. A standard sports drink provides fluid and carbohydrates for energy, while a small amount of brine supplies little fluid and no fuel, despite containing electrolytes lost through sweat.

Some runners who have already tested pickle brine during training may tolerate it and believe that it helps them. Brown advised athletes not to introduce the sour and salty drink for the first time during the marathon.

“I would not recommend trying pickle brine for the first time on race day,” she said. That caution is especially relevant because runners cannot know how their bodies will respond without having previously tried it during training.

If a severe cramp occurs and a runner decides to use pickle brine, Brown recommends taking small sips instead of drinking a large quantity at once. She also suggests gently stretching the affected muscle.

Athletes who are sensitive to acidic or salty beverages should exercise particular care, Brown added. Heat, fatigue and stomach upset can become greater concerns later in a race, potentially making an unfamiliar drink less appealing or harder to tolerate.

The promotion ultimately pairs McDonald's pickle brine with a practice that has enthusiastic followers but inconclusive scientific support. Fox News Digital contacted McDonald's for additional comment.