Some people work out simply because they enjoy working out. Others do it to improve their endurance or to build muscle. But many go to the gym to help them lose body weight.

Similarly, lots of people drink coffee because they enjoy it, or because they understand the health benefits of coffee. Many others, though, believe that drinking coffee will help them lose weight. Some evidence supports that belief.

That leads to an important question. Can exercise and coffee work together to provide even greater weight loss?

It might, according to a recent study published in the Journal of the International Society of Sports Nutrition.

Researchers had test participants perform timed sessions on exercise bikes. Before half of their sessions, they consumed three mg of caffeine per kilogram of body weight, about the same amount found in a cup of coffee. Before the other sessions, they took a placebo.

Here’s what the researchers found. Caffeine ingestion half an hour before exercise increased fat oxidation (that’s what most of us call fat-burning) at a much greater rate than was seen with the placebo. Exercise intensity (the amount of energy expended during exercise) was also greater for the test subjects who’d consumed the caffeine.

There were more discoveries, too. Caffeine’s benefits were strongest in the afternoon, not in the morning; fat-burning increased by 10% in the morning but by almost 30% in the late afternoon. Even more interesting: participants who exercised without caffeine in the afternoon burned the same amount of fat as those who exercised with caffeine in the morning. 

That leads to two conclusions.

• If you want to burn the most fat, you should exercise in the afternoon after drinking coffee.
• Combining coffee and exercise can boost fat-burning, and potentially, increase weight loss.

There’s some evidence that there are optimal times to drink coffee before a workout.

The effects of coffee start to kick in within 15 minutes of consumption, peak in about an hour and start to wear off 1-2 hours after that. Half of coffee’s caffeine is still in your body after six hours. So you’ll experience some benefits even if you’ve had your coffee several hours before hitting the gym.

However, that doesn’t mean you’ll experience optimal benefits.

We’ve already discussed one study that showed fat-burning was maximized 30 minutes after caffeine consumption. And the ISSN research review we mentioned earlier suggested caffeine’s benefits are greatest when it’s consumed 60 minutes before athletic performance.

A different study looked more specifically at the performance-enhancing benefits of caffeine for three forms of exercise.

It found that having coffee one hour before a workout is the right timing for both vertical jumps and so-called isometric exercises (like planks and squats) which don’t involve the joints. The right timing is 30 minutes, though, for isokinetic exercises like walking on a treadmill or riding an exercise bike, both of which do require the use of the joints.

The ISSN research suggests that the optimal amount of caffeine to consume before working out is 3-6 milligrams per kilogram of body mass, which is 1-2 cups of black coffee for most people. Separate research published in the Journal of Applied Physiology concurs, suggesting that two cups is the amount that helps most.

The type of coffee you drink before a workout only matters when it comes to caffeine content. One cup of coffee contains about 100 mg of caffeine, while a cup of instant coffee and a shot of espresso each contain about 60mg.

If you’re not a coffee drinker but still want caffeine before working out, most sodas contain around 30mg, and there’s a little less in tea. One can of Rockstar or Monster Energy should be enough for a pre-workout drink, since they each contain around 160mg of caffeine. Powdered pre-workout supplements have anywhere from 150-300 mg per serving.

Those ballpark numbers should help you decide the right amount to consume.

You probably already know whether you should avoid coffee before working out.

If you’ll only be consuming a cup or two, there’s no need to worry about caffeine overdose; it’s usually only an issue when you get higher than 400 milligrams per day.

The other potential side effects are simply the ones any coffee drinker might experience.

Anxiety or sleep difficulties usually occur only after high levels of consumption. Stomach aches might be a bigger issue, particularly on an empty stomach; drinking smaller amounts of very strong coffee or espresso before a workout could be a good solution.

Those who experience rapid heart rate or blood pressure after drinking coffee should naturally avoid it under any circumstances.

If you’re in that last group with caffeine sensitivity, you can get some of the same workout benefits by having a carb-heavy snack before exercising since carbohydrates provide additional energy and focus. Stay away from ones loaded with sugar, though, because they’ll lead to a sugar crash within an hour.