Does coffee really coat food that you just ate and neutralize the food's nutrients?

My friend heard from a guy who heard from his dad who’s a doctor that drinking coffee after breakfast coats the food you just ate, and this coating prevents the body from absorbing as many nutrients from the breakfast. He says that you should drink coffee before breakfast, not after. Is there any truth to this?



I was going to leave it at “No”, but also consider that coffee drinkers as a class are not malnourished and may even be chubby, depending on how many doughnuts they eat along with their coffee.

As far as i can tell from some quick internet research, it’s not that coffee “coats the food you just ate,” it’s that some of the ingredients in coffee, like caffeine, can hinder the body’s ability to absorb nutrients from food.

For example, from here:

And from here (PDF):

The second link also notes that:

There are also a couple of observations about the effects of coffee on nutrient absorption on this page, and a reference to a paper: Morck TA, Lynch SR, Cook JD. Inhibition of food absorption by coffee. Am J Clin Nutr 1983; 37; 416-420.

Given this information, it seems rather unlikely to me that drinking your coffee just before or just after your breakfast would make much of a difference. But i’m not a doctor, so i could be wrong about that.

From your first link:
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Not exactly a ringing endorsement, or an offer to stand behind their claims.

And from the second link:

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While ad hominem arguments will cost you points in a debate, in real life they are often timesavers. If someone believes things I know are a load of rubbish, they have to extend themselves pretty far to make me believe that the things they are telling me are true.

I am not a doctor either, but you don’t have to be a chicken to know when an egg is rotten.

On the other hand, this site, from the New York State Osteoporosis Prevention and Education Program says this:

"There may be a small decrease in calcium absorption associated with moderate caffeine consumption (up to 300mg of caffeine per day). In addition, there is minor increase in calcium loss in the urine for several hours after caffeine consumption. However, when the recommended amount of dietary calcium is consumed, the small decrease in calcium absorption and increase in calcium output caused by moderate caffeine intake can easily be offset. For example, the amount of caffeine in a cup of coffee can slightly reduce calcium absorption but adding a few tablespoons of milk can easily make up for it. "

Drink your coffee whenever you like, the data I’ve seen says that each cup of coffee results in the excretion of around 5 mg of calcium. As the RDA is 1000 mg, we’re not talking about a significant amount.

Which is precisely why i sought out my last link, which is from a university website and contains an extensive bibliography.

Also, your own citation specifically discusses calcium. It may surprise you to know that, when discussing the general issue of nutrient absorption, calcium is generally not the only nutrient that people want to know about.

I went online in my university’s database subscriptions to find the article i referred to above, from the American Journal of Clinical Nutrition. The abstract for the article states (no link as you need a subscription):

So, if the research and reporting in this article is right, while coffee might not impede iron absorption as much as tea, it still impedes it by about 40% if you drink coffee during or soon after a meal, but not if you drink coffee an hour before your meal.

I haven’t yet found any articles for other nutrients, and i don’t have time right now to do a laborious search, but there appears to be at least some support for the notion that coffee can impede absorption of one important nutrient when taken close to a meal.

Thanks, mhendo , nice cite. I’m on an Atkins diet, and never even consider iron as a nutrient of concern, but calcium, magnesium and potassium are problematic. I forget that my concerns aren’t everyone.

True, coffee, tea and some other dietary constituents or supplements can decrease iron absorption.

What needs to be taken into account is that coffee’s impact on most people who eat a normal diet is negligible. If you’re iron deficient from one of the common causes (i.e. hemorrhage or iron-poor diet) it would make sense not to drink coffee at mealtimes or when taking iron supplementation.

Any doctor who’d make a blanket statement about iron “coating” food and thus preventing or limiting nutrient absorption is likely a) misunderstood, b) ignorant, or c) a chiropractor. b) and c) are not mutually exclusive.