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After thorough research I have found that the only plausible reason for the “coffee with milk” myth was related to a number of studies showing that milk reduces the absorption/metabolism of chlorogenic acids (CGAs) available in coffee. I will, therefore, only address this topic.
The question asks specifically about mixing coffee with milk and so I will not be discussing the health risks of drinking cow’s milk. The health benefits and risks of each ingredient is another topic that is addressed in separate articles.
I also came across some complaints of stomach discomfort after drinking coffee with milk. These reports are usually quite vague and it is difficult to know whether the digestive issues are caused by other reasons:
- type of milk itself,
- quantity of milk,
- lactose contents in milk,
- type of coffee,
- quantity of caffeine, or
- time the drink is taken.
So far, the scientific literature does not mention any ill effects that this combination could cause and the anecdotal evidence is very weak to come to any such conclusions.
What is chlorogenic acid (CGA)?
Coffee contains polyphenols – powerful antioxidants with great health benefits. One of the most important polyphenols in coffee are called chlorogenic acids (CGA) which are associated with:
- antibacterial and anti-inflammatory properties and
- the reduction of the risk of blood pressure, cardiovascular disease, type 2 diabetes , colon cancer, hypertension and Alzheimer’s disease. (1, 2)
Of all the foods, chlorogenic acid is most abundant in green coffee beans.
The effects of drinking coffee with milk on CGAs levels
Studies on the effects of milk on CGAs in coffee beverages show mixed and contradictory results.
Two types of tests have been used to measure the CGAs: blood plasma vs. urine tests.
A 2010 study measured the blood contents of CGAs after mixing whole milk and non-dairy creamer and showed that (3):
- full cream milk doesn’t change CGAs levels in blood plasma.
- sweetened non-dairy creamer reduces CGAs in plasma by over 23%.
A study from 2011 looked at the amounts of CGAs and metabolites that are excreted in urine.
It found that after drinking coffee with a large quantity of milk, the amounts of CGAs and metabolites found in urine was 28% lower (a 23% decrease of CGAs alone). (4)
This study also concluded that:
- After drinking coffee with 200ml of milk, the amount of CGAs and metabolites in urine were (40% ± 27%);
- After drinking coffee with water, the amount of CGAs and metabolites in urine were (68% ± 20%). However, there are some issues with this study:
- It included only a small number of subjects (5 participants);
- The subjects had different capacities to absorb and metabolize these compounds;
- A minimum amount of milk that impacts CGA bioavailability was not measured. The experiment used 200mg of milk, however changing this amount could make a big difference in the result.
To summarize the available research, more and larger studies are needed to show more consistent results of the effects.
Is the 23% reduction in CGAs important?
Even if the urine study is correct, is this reduction relevant?
Let us consider some facts that will help interpret the results of the above research.
Aspect of CGAs bioavailability:
Considering that only by roasting coffee 70%-94% of CGAs are destroyed (depending on roast), 23% reduction of the remaining CGAs is not that significant anymore. If you enjoy coffee with milk, and at the same time want to insure high intake of CGAs, consider taking “green coffee bean extract”.
Please note, however, that dosages of CGAs have not been fully investigated and recommendations on the healthy and not harmful amounts cannot be made at this stage.
Any combination of foods can either reduce or improve the individual food properties’ health benefits. A milk and coffee combination is one of them. But we cannot take these findings out of proportion otherwise similarly we would have to obsessively eat many foods separately.
- If the sole purpose of drinking coffee is to have the benefit of CGA antioxidants, take CGA extracts from green coffee beans instead.
- If you enjoy coffee with milk, and don’t have any intolerance for each separately, go for it!
Impact for heavy coffee drinkers
If you are a heavy coffee drinker (around 6 cups of coffee per day), the amount of CGAs in your blood will be high and there is no reason to worry about a slight reduction.
You need to consider, however, that this amount of coffee may be too high for optimal health which includes both: too much coffee and too much milk.
If you have coffee with milk, you need to consider:
- the amount of milk you add,
- what kind of milk you use (full fat, skim) and
- if this impacts the overall balance of your diet.
If you are trying to lose weight you might consider drinking coffee without milk.
Some useful information about CGAs in coffee
- Modest to heavy coffee drinkers intake between 100mg – 2000mg of CGAs per day;
- Coffee abstainers’ intake less than 100mg of CGA per day; (5)
- The coffee we drink is made from roasted coffee beans. Although you can brew green (raw) coffee, drinking it wouldn’t be for pleasure. It simply tastes awful;
- Roasting coffee already loses 70%-94% of CGAs depending on the way it was roasted.
Here are some examples of concentration of CGAs between green bean and its roasted versions. From this example, you can see that the dark roasted coffee has already lost most of its CGAs. (6)
Green Arabica coffee: 4.6g /100g of dry beans
Lightly roasted Arabica coffee (used usually for filter coffees): 1.7g/100g
Dark roasted Arabica coffee (used usually for espresso machines): 0.3g/100g
Different levels of CGAs in coffees
Levels of CGAs vary between various products. (5):
- Roasted Arabica coffee (70-200mg per cup). Arabica represents about 70% of total world coffee consumption;
- Roasted Robusta coffee (70-350mg per cup). Robusta represents about 30% of total world coffee consumption;
- Decaffeinated coffee loses about 10% of CGA;
- Tea (20-60mg per cup);
- Example of Green (raw) coffee can contain 5-12g/100g CGAs (depending on bean type);
- Green coffee bean extract capsules may contain from 200mg-800mg CGAs.
We don’t really usually know how much CGAs we are getting from the coffee we are drinking especially because the concentration of CGAs varies considerably between different types of coffees (and teas). The concentration depends on several factors: (7, 8)
- Whether the coffee is brewed from green beans or from roasted beans;
- What type of bean varieties are used (e.g. Robusta has more CGAs than Arabica);
- Brewing methods;
- Time and temperature of roasting of beans.
NUTRITION FACTS VS NUTRITION MYTHS
You will find a summary of the most common nutrition myths and evidence-based nutrition facts here.