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What Effects Does Lactose Have on the Human Body?

author image Jan Annigan
A writer since 1985, Jan Annigan is published in "Plant Physiology," "Proceedings of the National Academy of Sciences," "Journal of Biological Chemistry" and on various websites. She holds a sports medicine and human performance certificate from the University of Washington, as well as a Bachelor of Science in animal sciences from Purdue University.
What Effects Does Lactose Have on the Human Body?
Two people have glasses of milk and cookies. Photo Credit Noel Hendrickson/Photodisc/Getty Images

A type of carbohydrate, you'll find lactose in milk and milk products. It is a disaccharide, or a sugar molecule, consisting of two sugars – glucose and galactose. In addition to dairy, lactose might also be in processed foods, because manufacturers add milk derivatives to products such as baked goods, pancake mix, processed meats and coffee creamers. Lactose can have both positive and negative effects on your body.


Carbohydrates are the macronutrients your body prefers as its primary energy source. Therefore, lactose can serve as fuel to power your activities. Once your body digests lactose, the sugars enter your cells, where they are metabolized for energy. Your body uses the energy to fuel your physical exercise and to maintain your basal metabolism. In addition, consuming lactose spares your dietary protein from serving as an energy source, allowing it, instead, to build muscle and perform its other maintenance functions.

Weight Gain

If the calories you take in outnumber the calories you burn, the excess stores as fat. For example, if you consume more lactose than you need, your body will convert the sugars it doesn’t burn to fatty acids. These fatty acids accumulate in your adipose tissue as an energy reserve. Therefore, a high lactose intake can result in weight gain, depending on your overall calorie expenditure. Excessive weight gain can lead to obesity, a condition of extreme overweight that increases your risk for cancer, cardiovascular disorders and type 2 diabetes.

Digestive Problems

Before your body can benefit from the energy contained in lactose, you must digest it to its constituent monosaccharides through the action of the digestive enzyme lactase. However, your intestinal cells may not make any, or enough, lactase to accomplish digestion. In this condition, called lactose intolerance, the undigested lactose traveling through your gastrointestinal tract can cause digestive upset. Common symptoms of lactose intolerance include abdominal pain, bloating, nausea, gas and loose stools.


To mitigate the negative effects of lactose on your body, you can adjust your diet depending on the problem this sugar causes. If the lactose you consume from milk products leads to excessive calorie consumption, you might need to reduce your intake or increase your physical activity level. If lactose causes digestive distress, you can either avoid high-lactose food products or take commercially available lactase supplements when consuming lactose-rich foods.

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