Working Out During the Baha'i Fast
A summary of scientific research

Several studies done on athletes who observed the Muslim fast of Rammadan yielded some loose guidelines for working out during a Rammadan-style fast. Of course, Rammadan is 30 days of not eating or drinking during daylight hours, while the Baha'i fast is only 19 days. Besides this major difference, however, the restrictions and exemptions are almost identical so I had confidence in using these studies as a reliable predictor of the effects of the Baha'i Fast on the body. 

First off, let's define the type of exercise that you may be looking to do. If you're thinking about a light walk in mild weather, practicing more meditative yoga, or doing some tai chi, then these guidelines don't apply. Here's an easy way to check: if you work up a sweat, become out of breath, or get very thirsty during your workout, then these guidelines apply: 

1) Wake up before dawn and eat breakfast

In Dr. Fereidoun Azizi's review article in the Annals of Nutrition & Metabolism in 2010 entitled "Islamic Fasting and Health" he highlighted the importance of not missing the predawn breakfast as it helps to maintain normal levels of glucose processing by the body, a necessity for fueling your muscles during a moderate to difficult workout. 

2) Work Out After Breaking the Fast to Avoid Fatigue During Workout

In order to have an intermediate to strenuous work out without excessive fatigue or feeling light-headed, it was recommended that some carbohydrate and water be consumed during the workout (Maugan et al., 2010. "The effects of fasting on metabolism and performance". Br J Sports Med 44: 490-494). So if you're thinking of doing a decently hard workout, break the fast with half of an energy bar, or half of a greek yoghurt or even a small piece of bread with some peanut butter, and some water. Keep the water or sports drink nearby and sip while working out as it has been shown that not drinking any fluids during your workout will negatively affect performance (Maugan et al., 2010. "The effects of fasting on metabolism and performance". Br J Sports Med 44: 490-494).

3) Refuel With Protein & Complex Carbs After Your Workout

Another strong argument for working out in the early evening right after breaking the Fast is the fact that most sports nutritional guidelines recommend proper refueling of your body after working out. This helps to "promote recovery and to stimulate the process of adaptation taking place within the exercised muscles" as well as replacing lost fluids and electrolytes if it's been a significant sweat session (Maugan et al., 2010. "The effects of fasting on metabolism and performance". Br J Sports Med 44: 490-494). What you eat after working out is just as important as when you eat it. Eating some protein and carbohydrates in the first 4 hours after working out enhanced glycogen synthesis, which helps muscles repair and strengthen immediately after exercise (Burke. 2010 "Fasting and recovery from exercise." Br J Sports Med 44: 502-508). You don't have to consume a lot of carbohydrates and protein in order to promote recovery. A regular sized helping (1-2 cups) of couscous, pasta, rice, sweet potato, potato or bread with at least one cup of protein  in the form of lean meat, eggs, beans, yoghurt or cheese should be plenty to replenish your energy stores and help your muscles recover. And don't forget to drink lots of water!