What you should eat before exercise depends on your blood sugar level at that moment, the type of workout you’re doing, and how long you plan to be active. The general rule: check your blood sugar first, then decide. If it’s below 150 mg/dL, you need a carbohydrate-containing snack. If it’s above 150 mg/dL, you can typically start exercising without one.
Check Your Blood Sugar First
Your pre-exercise blood sugar reading determines whether you need food, how much, and what kind. The ideal range before a workout is between 90 and 250 mg/dL. Here’s how to respond at each level:
- Below 90 mg/dL: Your blood sugar is too low to exercise safely. Eat 15 to 30 grams of fast-acting carbohydrates (fruit juice, glucose tablets, crackers) and wait before starting. Short or very intense activities under 30 minutes, like weight training or intervals, may not need as much.
- 90 to 150 mg/dL: Have a snack with about 15 to 30 grams of carbohydrates before you begin. For longer sessions, plan on roughly 0.5 to 1.0 grams of carbohydrate per kilogram of body weight for each hour of exercise.
- 150 to 250 mg/dL: You’re in a good range to start. Hold off on eating until your blood sugar dips below 150 during the workout.
- Above 250 mg/dL: Test for ketones before doing anything. If ketones are moderate or high, skip the workout entirely. If they’re negative or only trace amounts, stick to mild or moderate activity and avoid intense exercise until your levels come down.
These thresholds matter most for people with type 1 diabetes, who face a higher risk of blood sugar swings during activity. If you have type 2 diabetes and aren’t on insulin, the risk of exercise-induced lows is smaller, but checking beforehand is still a smart habit.
What Makes a Good Pre-Workout Snack
The ideal pre-exercise snack is built mostly around carbohydrates, with a small amount of protein and minimal fat. Carbs are the fuel your muscles pull from most readily during activity, and protein helps slow the release of glucose so you don’t spike and then crash. Fat slows digestion too much before a workout and can leave you feeling sluggish.
For a moderate workout lasting around 45 minutes, about 15 grams of complex carbohydrates eaten 15 to 30 minutes beforehand is a solid starting point. If you’re planning something longer than 30 minutes, bump that up to 30 grams. Some practical combinations:
- Apple slices with a tablespoon of peanut butter: Gives you carbs from the fruit and a small protein boost from the nut butter.
- Whole-grain crackers with cheese: A piece of low-fat string cheese or ricotta on a few crackers keeps the carb count manageable.
- Plain yogurt with fresh fruit: Light on carbs, provides protein, and works well as a quick pre-workout option.
- A small handful of nuts with a piece of fruit: Almonds, walnuts, or pistachios paired with a banana or a few dried apricots.
- Hummus with whole-grain crackers or veggie sticks: About a third of a cup of hummus gives protein and fiber without a big carb load.
If your blood sugar is genuinely low (under 90 mg/dL), reach for something faster-acting first: fruit juice, glucose gels, or regular crackers. These get sugar into your bloodstream within minutes. You can follow up with a more balanced snack once your levels stabilize.
Timing Your Snack
Eating about 30 minutes before exercise appears to be the sweet spot. That window aligns with when digested glucose begins entering your bloodstream most actively, giving you fuel right when you need it. Eating too close to your workout, say five minutes before, means the food hasn’t had time to do much. Waiting more than an hour means the glucose peak may have already passed.
If you’re eating a larger meal rather than a snack, give yourself more time. A full meal with carbs, protein, and some fat needs one to two hours to settle. For most people planning a workout, a small snack 15 to 30 minutes before is more practical than trying to time a full meal perfectly.
How Exercise Type Changes What You Need
Aerobic exercise, like walking, jogging, cycling, or swimming, tends to pull blood sugar down. The longer and steadier the activity, the more glucose your muscles use. This is where pre-exercise carbohydrates matter most, because a 45-minute jog can cause a meaningful drop.
Strength training and high-intensity interval training often have the opposite effect. These activities trigger stress hormones that temporarily push blood sugar up. If your blood sugar is already between 180 and 270 mg/dL, lifting weights or doing sprints may raise it further. In that case, you likely don’t need a pre-workout snack at all.
For mixed workouts that combine cardio and weights, start with your blood sugar reading and lean toward having a small snack if you’re below 150 mg/dL. The cardio portion will pull glucose down even if the strength work briefly raises it.
Hydration Before and During Exercise
People with diabetes face a higher risk of dehydration because elevated blood sugar pulls extra water into the kidneys. Starting your workout well-hydrated is just as important as eating the right snack.
In the hour before exercise, aim for about 200 to 300 mL of water (roughly 7 to 10 ounces). Adding a splash of diluted, no-sugar-added fruit juice can help with flavor and provide a small amount of glucose. For any workout under 90 minutes, plain water is enough. If you’re going longer than that, or exercising in heat, switch to an isotonic sports drink that includes electrolytes.
A quick way to gauge your hydration status: check your urine color. Pale yellow, like lemonade, means you’re in good shape. Darker, like apple juice, means you need more fluids before starting. After your workout, a rough guideline is to drink about 500 mL (roughly 17 ounces) for every hour of exercise.
Evening Exercise and Overnight Lows
If you exercise in the evening, your blood sugar can continue to drop for hours afterward, raising the risk of low blood sugar while you sleep. This delayed effect happens because your muscles keep replenishing their energy stores long after the workout ends, pulling glucose from your bloodstream in the process.
A bedtime snack with complex carbohydrates and some protein can help buffer against overnight lows. Something like whole-grain toast with peanut butter or yogurt with a small amount of granola provides a slow, steady release of glucose through the night. Checking your blood sugar before bed and setting an alarm for a mid-sleep check may also be worthwhile after particularly intense evening sessions, especially if you have type 1 diabetes.
Type 1 vs. Type 2 Considerations
If you have type 1 diabetes, pre-exercise nutrition requires more precision. Because you’re managing insulin doses externally, the interplay between food, insulin, and activity is more volatile. The carbohydrate guidelines above (15 to 30 grams based on blood sugar level) were developed primarily with type 1 in mind. You may also need to adjust your insulin dose before a workout, which is something to plan with your care team.
If you have type 2 diabetes, particularly if you manage it through diet and oral medications rather than insulin, the risk of exercise-induced hypoglycemia is lower. You still benefit from a pre-workout snack if your blood sugar is under 150 mg/dL, but you generally have more flexibility. The bigger priority for type 2 is consistency: regular physical activity, ideally 150 minutes per week of moderate aerobic exercise plus two to three strength sessions, improves insulin sensitivity over time and makes blood sugar easier to manage overall.