Is Milk Fast Digesting? (A Dietitian Answers)

Determining whether milk is fast digesting can be difficult, as the nutritional composition can differ significantly between different types of milk.

As a dietitian, my job is to educate people on how to differentiate between milk products that are faster-digesting and those that are slower-digesting to help them reach their goals.

Here’s my quick answer:

Dairy and soy milk are slow digesting because they contain higher amounts of protein and fat. Coconut, rice, oat, and nut milk, particularly if sweetened, are fast digesting since they are high in sugar, low in protein, and have variable fat contents.

Knowing the differences in digestion rates between different types of milk products will help you choose the best milk product for your health and performance goals.

Key Takeaways

• Dairy milk contains casein, which is one of the slowest digesting proteins. It is also a complete protein, making it optimal for muscle recovery and growth.
  
• Although plant-based milk does not contain all of the essential amino acids, it can be easily combined with complementary food sources to become a complete protein.

• Milk typically digests within 1-4 hours, depending on its nutrient profile. It can easily be added to pre and post-workout meals, or a snack during the day or before bedtime.

Understanding the Glycemic Index

The Glycemic Index (GI) is a tool used to understand how carbohydrate-rich foods impact blood glucose (sugar). Each food receives a score between 1 and 100 to reflect how quickly it raises your blood sugar.

Foods that digest more quickly will raise blood sugars more rapidly, whereas foods that take longer to digest will result in a slow and steady rise in blood sugar.

GI scores are classified as follows: low (1-55), medium (56-69), and high (70-100). Foods assigned with higher scores indicate a rapid rise in blood sugars, while lower scores indicate a more gradual rise in blood sugars. 

Although the GI is useful for comparing foods based on how quickly they affect blood sugars, there are also other dietary factors impacting blood sugars, such as the amounts of carbs, protein, and fat in foods, and portion sizes. 

How Long Does It Take Milk To Digest?

Based on the different nutrient compositions between dairy milk, non-dairy milk, reduced-fat milk, and fat-free milk, the digestion time of milk varies, ranging from 1-4 hours.

Most dairy and soy milk is typically low GI since it contains a mix of nutrients (carbs, fat, and protein), while other plant-based sources often lack protein and contain added sugars which makes them faster digesting.

The fat content of the milk will also play a role in how quickly it digests, with higher fat intakes causing slower rates of digestion. 

Take skimmed cow’s milk and whole cow’s milk as an example. 

Skimmed milk (fat-free) undergoes faster digestion compared to whole (4%) cow’s milk because fat digests at a slower rate.

The digestion time will also change if you pair milk with other foods. If you add 200ml of milk to a fruit and oat smoothie, then this will digest slower than if you drink milk on its own.

This is because fruit and oats contain other nutrients (fiber, starch, and fat) that slow down the digestion of the whole meal and there is more food to digest at one time.

• Related article: What Are Fast Digesting Foods? 10 Examples & When to Eat

Is Milk a Slow or Fast Digesting Protein?

Dairy milk is considered a slow-digesting protein because it has more casein than whey and it is also considered low GI because the protein and fat content of milk slows its digestion.

There are two types of protein found in dairy milk: casein (80%) and whey (20%), with whey being a faster-digesting protein than casein. 

So if you compare a glass of cow’s milk with a whey protein shake, milk will digest slower since it is 80% casein.

Since milk has a higher amount of carbs, it’s impossible to rank the rate of digestion solely based on its protein digestion rate; which is why it’s typically classified based on its GI rating.

This is opposite to whey protein powder which doesn’t have a GI rating and is classified exclusively based on its protein digestion rate.

Another important consideration for the rate of digestion of milk is the difference between dairy milk and plant-based milk.

Animal protein in dairy milk is generally easier to absorb and digest than plant protein in nut, soy, and grain-based milk products (unless you’re lactose intolerant), making it faster to digest from a protein point of view.

This is because, unlike animal proteins, plant proteins contain a fibrous coating that the body has to work harder to digest. 

Animal protein absorption rate is also 10-20% higher than that of plants, meaning that the body finds it easier to break down and absorb protein in dairy. 

For example, you will likely absorb more protein from 200 ml of cow’s milk compared to 200 ml of soy milk.

Digestion Rate Of Milk vs Other Protein Sources

So, how does the GI of milk products (containing protein) compare to other mixed macro foods containing carbs and protein?

The following table shows a few different types of protein-rich foods with their GI score, according to the International tables of glycemic index values.

*Remember that low GI foods are 1-55, medium GI foods are 56-69, and high GI foods are 70+. 

As you can tell, both milk products (cow’s milk & soy milk) are slow digesting and their GI is similar to the other foods which are also low GI. This can be attributed to their composition, which includes a combination of carbs, fats, and protein. 

Compared to carbs, protein, and fat are digested at a slower rate, contributing to the overall slower digestion of these products. 

Types of Milk: Ranking From Fastest To Slowest Digesting

According to the International tables of glycemic index values, cow and soy milk have a low GI. However, other plant-based milk products have a high GI, likely due to the added sugar and low protein and fat content.

The following table shows the GI score of different types of milk (dairy and non-dairy).

*Low GI foods are 1-55, medium GI foods are 56-69, and high GI foods are 70+.

*This value was taken from an in-vitro study (test-tube experiment) and not from human subjects

Based on these ranges, dairy and soy milk have the lowest GI and digest the slowest, while sweetened oat, coconut, and rice milk have the highest GI and digest the fastest.

Benefits of Consuming A Slow Digesting Protein Like Milk

The benefits of consuming a slow-digesting protein like milk are:

1. Provides A Variety Of Nutrients

Dairy milk offers a wealth of essential nutrients that play a vital role in maintaining overall health.

It contains all essential amino acids which the body needs to promote muscle growth and repair (including branched-chain amino acids isoleucine, leucine, and valine to stimulate muscle building and recovery).

Furthermore, it is worth noting that the sugars found in unflavored dairy are naturally present and do not contribute to your daily intake of added sugars.

2. Versatile Energy Source

Milk offers versatility in terms of the type of energy it delivers, whether it be fast-acting or slow-acting.

When you opt for full-fat and protein-rich milk, it provides more stable energy. On the other hand, low-fat, low-protein, and high-carb (sugar) milk results in fast-acting energy.

Drawbacks of Consuming A Slow Digesting Protein Like Milk

The drawbacks of consuming a slow-digesting protein like milk are:

1. Can Be High In Added Sugar

Certain flavored plant-based varieties, like rice, oat, and coconut, can have high levels of added sugar, leading to a spike in blood sugar. 

Consistently consuming high-GI milk products, along with processed foods like cake, juices, and candy, can pose long-term health problems, such as increasing the likelihood of developing insulin resistance (when your body struggles to extract sugar from the blood to use as energy). 

For individuals with diabetes, consuming fast-digesting carbs is also unfavorable as it can result in unregulated blood sugar levels.

2. Not Filling

Due to their low content of “filling” nutrients such as resistant starch and fiber, milk does not provide prolonged satiety (unless paired with other foods). Consequently, it may not keep you feeling full for long. 

This lack of satiety can be problematic when trying to lose weight, as it may cause you to consume more calories than you would if you had a more filling source of carbs.

When Should You Drink Milk?

Milk can be consumed at any time depending on one’s preferences, but here are some scenarios when it might be more advantageous to drink milk:

• Pre-workout: consider having fat-free or low-fat milk (skimmed dairy, rice, or oat) approximately 60-90 minutes before your workout, paired with a carb-rich meal to give you energy to fuel your workout. Limiting fat is important since it takes long to digest (3-4 hours).

• Post-workout: dairy or soy-based milk are ideal since both are good sources of protein and sugars. Combining these types of milk with carbs and a bit of extra protein creates an ideal post-workout recovery meal that helps restore the energy lost during exercise. 

• 30 minutes before sleep: milk before bedtime can help to facilitate muscle recovery and inhibits protein breakdown during sleep since it is rich in casein (a slower digesting form of protein). The ideal portion is around 30-40g of casein protein.

• As a snack or as part of breakfast: dairy or plant-based milk varieties can be paired with cereal, or oatmeal, or consumed on their own as a source of nutrients in between meals or at breakfast. 

Related: Can You Mix Milk With Whey Protein?

How To Make Milk Digest Faster or Slower

1. Drink It By Itself

To make milk digest faster, drink it on its own. This promotes faster digestion as it would not have to be broken down with other foods, which would make the digestion process slower.

2. Choose A Higher Fat And Protein Milk

If you prefer a slower digesting milk, choose a type that provides higher protein and fat content. Some examples include cow’s milk and soy milk. To make it digest even slower, have it with a snack (i.e. nuts in a yogurt pot) or add it to a smoothie.

• Related: 10 Low-Calorie Milk Options

3. Have A Sweetened/Flavored Plant-Based Milk

For milk to digest faster, choose a type that is sweetened and with added sugars, which is commonly low in fat and has lower protein content. A good example is coconut, oat, or rice milk (different brands have different flavors, such as hazelnut, chocolate, and vanilla).

References

Jeske, S., Zannini, E., & Arendt, E. K. (2017). Evaluation of Physicochemical and Glycaemic Properties of Commercial Plant-Based Milk Substitutes. Plant foods for human nutrition (Dordrecht, Netherlands), 72(1), 26–33. https://doi.org/10.1007/s11130-016-0583-0

Carbone, J. W., & Pasiakos, S. M. (2019). Dietary Protein and Muscle Mass: Translating Science to Application and Health Benefit. Nutrients, 11(5), 1136. https://doi.org/10.3390/nu11051136

Kim J. Pre-sleep casein protein ingestion: new paradigm in post-exercise recovery nutrition. Phys Act Nutr. 2020 Jun 30;24(2):6-10. doi: 10.20463/pan.2020.0009. PMID: 32698256; PMCID: PMC7451833.

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About The Author

Giulia Rossetto is a qualified Dietitian and Nutritionist.

She holds a Masters in Human Nutrition (University of Sheffield, UK) and more recently graduated as a Dietitian (University of Malta).

Giulia aims to translate evidence-based science to the public through teaching and writing content. She has worked 4+ years in clinical settings and has also published articles in academic journals.

She is into running, swimming and weight lifting, and enjoys spending time in the mountains (she has a soft spot for hiking and skiing in the Italian Dolomites).