Is lactose as bad as other sugars?

December 16, 2025 •

4 min read

According to estimates, approximately 65-70% of the world's adult population experiences some form of lactose maldigestion. This raises a key question: is lactose as bad as other sugars, or does it have unique characteristics that differentiate it from more commonly villainized sweeteners?

Quick Summary

This article explores the fundamental metabolic distinctions between lactose and other common sugars like fructose and sucrose, evaluating their comparative health impacts. It covers lactose's unique benefits, the reality of lactose intolerance, and offers a balanced perspective on its role in nutrition.

Key Points

Lactose is a unique natural sugar: Unlike added sugars such as sucrose, lactose is naturally found only in milk and is not as sweet.
Lower glycemic impact: Lactose has a lower glycemic index than most common added sugars, leading to a slower, more moderate rise in blood sugar.
Promotes gut health: For some, undigested lactose acts as a prebiotic, stimulating the growth of beneficial gut bacteria like Bifidobacteria.
Enhances mineral absorption: Lactose aids in the absorption of key minerals, particularly calcium and magnesium, especially in infants.
Less harmful to teeth: Lactose is less cariogenic than other sugars, meaning it is less likely to cause tooth decay.
Lactose intolerance is distinct from sugar's metabolic harm: The issue with lactose for many adults is a digestive intolerance due to lactase deficiency, not the same metabolic damage caused by excessive added sugars.

What is Lactose and How is it Digested?

Lactose, often called 'milk sugar,' is a disaccharide found in mammalian milk, including cow's and human breast milk. It is composed of two simpler sugar molecules, glucose and galactose, joined together. For the body to use lactose for energy, it must be broken down by the enzyme lactase in the small intestine. The glucose and galactose are then absorbed into the bloodstream. In many adults, however, the production of lactase decreases after infancy, leading to lactose malabsorption and potential intolerance. When undigested lactose reaches the large intestine, it is fermented by bacteria, causing common digestive symptoms like gas, bloating, and diarrhea.

Lactose vs. Other Common Sugars: A Metabolic Comparison

To understand if lactose is 'bad,' it's crucial to compare it with other sugars. Common added sugars, like sucrose (table sugar) and high-fructose corn syrup (HFCS), behave very differently in the body. Sucrose is a disaccharide of glucose and fructose, while fructose is a monosaccharide (simple sugar) found in fruit.

Glycemic Index and Blood Sugar

One of the most significant differences lies in the glycemic index (GI), a measure of how quickly a food raises blood sugar levels.

Lactose: Has a relatively low GI, with estimates ranging from 46 to 65. Its slower digestion is due to the extra step required to convert galactose to glucose in the liver, resulting in a less rapid blood sugar spike compared to pure glucose.
Sucrose and Glucose: Both have a higher GI than lactose, causing a quicker and more pronounced spike in blood glucose and insulin levels.
Fructose: Has a very low GI (19-27), as it doesn't directly stimulate insulin release. However, excessive intake can lead to other metabolic issues.

Health Implications of Fructose and Sucrose

While lactose intolerance is a digestive issue, high intake of added sugars like sucrose and fructose is linked to chronic metabolic diseases. Excessive fructose, particularly from added sweeteners like HFCS, is metabolized almost entirely by the liver. When consumed in excess, this can lead to increased fat production, raising the risk of fatty liver disease and insulin resistance. In contrast, lactose's slower digestion and low GI make it less prone to causing these metabolic stresses when consumed in moderate amounts.

Beyond Digestion: The Health Benefits of Lactose

Beyond being a simple energy source, lactose offers unique nutritional advantages that other sugars do not. These benefits are particularly pronounced in infants but also apply to lactase-persistent adults and, to some extent, even those with mild malabsorption.

Gut Health and Probiotics

For many, undigested lactose acts as a prebiotic, nourishing beneficial gut bacteria.

Lactose that reaches the colon is fermented by gut microbes like Bifidobacteria and Lactobacilli.
This process produces beneficial short-chain fatty acids (SCFAs), which are crucial for maintaining gut barrier integrity and supporting immune function.
This is in stark contrast to high-sugar diets, which can promote less desirable bacterial overgrowth.

Mineral Absorption

Lactose has a documented role in enhancing mineral absorption, especially for calcium and magnesium. This effect is particularly significant in infants, where lactose-derived organic acids may lower intestinal pH, increasing mineral solubility. While the effect is less pronounced in healthy adults, it is a testament to lactose's unique nutritional value.

Low Cariogenic Potential

Unlike highly fermentable sugars like sucrose, lactose is significantly less cariogenic, meaning it is less likely to cause dental caries or tooth decay. The slower acid production from lactose fermentation and milk's natural buffering capacity help protect against enamel erosion.

Lactose Intolerance: What You Need to Know

Lactose intolerance is not an allergy; it is a digestive issue caused by an insufficient amount of the lactase enzyme. Symptoms vary in severity based on the individual's lactase levels and the amount of lactose consumed.

Understanding Malabsorption

Primary Lactose Intolerance: The most common type, where lactase production naturally declines after childhood.
Secondary Lactose Intolerance: Caused by injury, illness, or surgery affecting the small intestine.
Managing Symptoms: Many intolerant individuals can manage symptoms by controlling portion sizes, consuming dairy with other foods, or using lactase enzyme supplements. Avoiding dairy completely can lead to deficiencies in calcium and vitamin D if not replaced through other dietary sources or supplements.

Comparison of Lactose and Added Sugars


Feature	Lactose (Milk Sugar)	Added Sugars (e.g., Sucrose, Fructose)
Source	Naturally in milk and dairy products	Extracted from plants (cane, beets) and added during processing
Composition	Glucose + Galactose	Sucrose: Glucose + Fructose
Digestion	Requires lactase enzyme	Requires sucrase enzyme for sucrose
Glycemic Index	Low (46-65)	High (Sucrose 68-92, Glucose 100-138)
Blood Sugar Impact	Slower, less pronounced rise	Rapid, higher spikes
Gut Health	Can act as a prebiotic, favoring beneficial bacteria	Can negatively impact gut microbiota balance
Other Benefits	Enhances mineral absorption (calcium, magnesium)	None beyond energy; high intake is harmful
Dental Health	Low cariogenic potential	High cariogenic potential
Associated Health Risks	Gastrointestinal discomfort in intolerant individuals	Obesity, insulin resistance, metabolic syndrome with excess intake

Conclusion: Is Lactose Really as Bad as Other Sugars?

Based on the scientific evidence, lactose is fundamentally different from and arguably not 'as bad as' other sugars, especially added sucrose and high-fructose corn syrup. While lactose can cause digestive problems for those who are intolerant, it offers unique health benefits, including a lower glycemic impact, mineral absorption enhancement, and prebiotic effects. Its status as a naturally occurring sugar within a nutritious food matrix (dairy) is key. The health risks associated with excessive added sugars—including rapid blood sugar spikes, dental decay, and liver strain—are not mirrored in lactose consumption, provided it is tolerated by the individual. Therefore, for most people, managing lactose intake due to intolerance is a matter of dietary adjustment, while minimizing consumption of added sugars is a critical health priority.

For more detailed information on managing dietary issues, consider consulting trusted health resources like the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Frequently Asked Questions

Lactose is a disaccharide of glucose and galactose found naturally in milk, with a low sweetness profile. Table sugar, or sucrose, is a disaccharide of glucose and fructose, often added to foods for a sweet taste and linked to more negative health effects when consumed in excess.

Yes, lactose can enhance the intestinal absorption of minerals like calcium and magnesium, an effect particularly observed in infants. This helps support bone health.

Yes, many individuals with lactose intolerance can consume small amounts of lactose without symptoms. Products like hard cheeses and yogurt have lower lactose content, and lactase supplements can also help manage digestion.

Lactose has a lower glycemic index compared to glucose and sucrose, causing a slower rise in blood sugar. However, individuals with diabetes should monitor their overall carbohydrate intake and discuss specific dietary needs with a healthcare professional.

'Low cariogenicity' means that lactose is less likely to contribute to tooth decay compared to other sugars. This is because it is not fermented as rapidly by oral bacteria, and the other components of milk, like calcium, also help protect teeth.

In individuals with reduced lactase, undigested lactose acts as a prebiotic, nourishing beneficial bacteria like Bifidobacteria in the gut. This fermentation can produce beneficial short-chain fatty acids.

Lactose-free products are created by adding the lactase enzyme to break down the lactose, making them easier to digest for those with intolerance. They typically have a similar nutritional profile to regular dairy, so 'healthier' depends on the individual's ability to tolerate lactose.