While we don’t judge, Dimity and I are always slightly aghast when we meet a mother runner who tells us she ran a marathon or completed a long training run without taking in any calories. We’ve run long and far enough–and interviewed enough sports dieticians and nutritionists–to know you’ve got to give your engine fuel (read: carbohydrates) to stay strong. For us, GU Energy Gels, in a panoply of flavors, works best, so here’s the 411 on how to do a GU.

-If you’re going to be running longer than 60 to 75 minutes, plan on ingesting a packet of GU every 45 minutes on your run. (If you prefer chewing rather than slurping, opt for four GU Chews instead.) E.g. When running for two hours, suck down a GU 45 minutes into your effort, then take another one at the 90-minute mark.

-If your calorie-flame burns brightly (usually happens in highly trained athletes, those lucky ducks), you can take in a GU every half-hour. But don’t take in more than about 350 calories/hour (each packet o GU has 100 calories; four GU Chews have 90 calories) as thats tough on the gut and diverts blood from hard-working muscles.

-Don’t eat just half a packet: A packet of GU is formulated to be consumed all at once, and an open pack is just a mess waiting to happen. (Think frosting + baby’s first birthday.) If you really only want, say, 50 calories, chew a few instead.

-Drink liquid whenever you ingest a GU–it helps your body absorb the carbohydrate-goodness in the gel. Don’t double-down on carbs, though: Water or a low-cal electrolyte drink is ideal.

-Unless you’re a pro at rubbing your head and patting your belly, or other multi-tasking moves, walk as you take a GU and follow it with a liquid chaser.

-Experiment with different flavors. There’s a veritable farm stand of fruit flavors, a variety of chocolate-y sweet ones, coffee-inspired ones, and the wildly popular Salted Caramel. Prefer plain? Opt for Tastefully Nude.

-Stash a packet in your bra, pocket, or hand to warm it up. Not crucial, but warm GU slides down easier. Especially true in colder months. So when I know I’m taking a GU at Mile 4 of half-marathon, I clutch one in my hand or stuff a packet in my bra around Mile 3. (But don’t carry gel packets in your sports bra the entire race unless you are looking for chafed cleavage!)

-Give yourself an extra jolt with a caffeinated GU. Studies have shown caffeine can lessen pain during exertion, allowing you to push harder or at least not feel so draggy. GU Espresso Love (Dim’s fav flav) has 40 mg caffeine (that’s roughly equivalent to the jolt provided by 4 ounces of java), while most flavors have 20 mg. Strawberry Banana, Lemon Lime, Root Beer, and Peanut Butter are the only non-caffeinated flavors. Pull out your reading glasses to see caffeine content printed on the “neck” of each GU Energy Gel packet.

-Bring at least one more packet than you think you’ll need. Whether you fumble one mid-race or start feeling wonky in the final mile or two, you’ll be glad to have an extra GU to fire you up.