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Why Is My Blood Sugar Low After Eating?

Natalie Stein
October 9, 2020
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Have you ever been engaged in something, feeling fine, when – wham! – you feel like something hit you? Suddenly, you may be shaky, weak, and confused. This can be a sign of low blood sugar, and it can happen even after eating.

What Is Low Blood Sugar?


Low blood sugar is a level of sugar, or glucose, in the blood that is lower than normal. The usual cut-off value for low blood glucose is 70 mg/dl, but you may not be measuring your blood sugar if you have not been diagnosed with diabetes. Instead, you might recognize it from its symptoms. The fatigue, fuzzy thinking, and need to sit down are the result of your body being deprived of its main fuel source: glucose.

Sources of Blood Sugar


You need to maintain a certain level of glucose, or sugar, in your blood to use for energy. That glucose can be derived from the foods you eat, especially those high in carbohydrates (sugars and starches). When you have not eaten for a while, your liver can release some glucose to maintain blood glucose levels and energy. 

Rebound Hypoglycemia After Eating


If sugar comes from the food you eat, why would blood sugar be low after eating? It may be due to a phenomenon called reactive hypoglycemia. This refers to low levels of blood glucose that “react” to high levels.

Say breakfast includes pancakes, syrup, and fruit juice. The meal is full of carbs: starch in the pancakes, added sugar in the syrup, and natural sugar in the fruit juice. Those carbohydrates get absorbed fast.

Blood sugar can skyrocket, especially in people who have prediabetes or diabetes. You may feel a sugar high, or burst of energy, within minutes to an hour of eating. Then…the crash. “The higher they fly, the harder they fall,” is spot-on for blood sugar. If it went up, up, up, it will go down, down down, possibly below normal levels and into the range of “hypoglycemia.”

Who Gets Low Blood Sugar?


Low blood sugar can happen in people with prediabetes or diabetes.If you are on insulin, it can happen if you take more insulin than you need, skip a meal, or eat fewer carbohydrates than usual without adjusting insulin. If you are not on insulin, or have diabetes but do not know it, low blood sugar can also happen if you skip a meal. It can also happen if you exercise more than usual. 

Low blood sugar is also more likely after eating meals that are high in starches and sugars because these are types of carbohydrates that raise blood sugar levels quickly. The effect is greater if the meal is low in protein, fat, and fiber, since those nutrients slow digestion and prevent blood sugar from swinging so wildly.

How to Prevent Low Blood Sugar


Small changes to your diet and physical activity habits can help prevent blood sugar spikes and decreases.

  • Take smaller portions of high-carb foods, such as bread, pasta, potatoes, desserts, soft drinks and other sugar-sweetened beverages, and rice.
  • Include a source of protein, fat, and/or dietary fiber when you eat carbohydrates.
  • Choose less-processed versions of foods, such as whole fruit instead of juice, whole grains instead of refined, and pasta al dente instead of very well-cooked pasta.
  • Instead of exercising on an empty stomach, have a small snack an hour or two before you start, or a larger snack or small meal three hours before.
  • Have a snack or your next scheduled meal as soon as possible after exercising.

These changes can help prevent blood sugar swings.

Instead of… Try… Because…
White bread with jam
Whole-grain bread with peanut butter and fruit
Jam adds sugar, fruit and whole-grain bread add fiber, and peanut butter adds fat and protein.
Bean and rice burrito
Bean and cheese or chicken burrito on a whole-wheat tortilla
Rice and a tortilla add carbs, while swapping chicken or cheese adds protein.
Boiled potato
Baked potato skins with Greek yogurt and broccoli
The skins have fewer carbs while yogurt adds protein and broccoli adds fiber
Fruit smoothie
Fruit salad with cut fruit (or berries) and walnuts
Cut fruit is lower in fiber than pureed, and walnuts have protein, fat, and fiber
Pancakes with syrup and fruit juice
Pancakes with cut fruit (or berries) and cottage cheese
Fresh fruit adds fiber, and cottage cheese adds protein
Apple-cinnamon flavored instant oatmeal
Steel-cut or plain oatmeal with diced apples and cinnamon
Flavored oatmeal is packed with added sugar, while apples have fiber.
Pretzels and a soda
Brown rice cakes and cheddar cheese
Soda adds sugar, while brown rice cakes add fiber and cheese adds fat and protein

Know Your Prediabetes Risk


If you think you may have low blood sugar sometimes, it may be time to speak to your healthcare provider and to take the Prediabetes Risk Test. If you are at risk for diabetes, Lark Diabetes Prevention Program can help lower that risk by coaching you on simple lifestyle changes.

Author
Natalie Stein

Exercise, Fitness & Nutrition Expert | Lark Health