The milk controversy

Healthy Eating Plate - Harvard

Since Harvard University switched their version of the Healthy Eating Plate for another one that limits the dairy there has been hell up.

Harvard defended at the time that although calcium is essential for healthy bones, we can obtain it from other sources. They also highlighted how dairy consumption seems to increase the risk of prostate and ovarian cancer and are rich in saturated fats and retinol, which in high amounts could be dangerous. 

Since then the anti-dairy movement has really gathered pace, telling us dairy products are pro-inflammatory, that the world wide population are lactose intolerant, that the countries with higher per capita dairy intake have higher rates of osteoporosis and that dairy contribute to weight gain.

However, if we delve into the evidence what does it actually tell us?


Let's start from the beginning: milk or dairy ARE NOT essential for our health (although calcium is). We can obtain calcium from other sources such as green leafy vegetables and nuts. If you check out this study, Weaver et al (2) studied the bio-availability of calcium in milk and compared it with that of calcium in vegetables. Afterwards, they compared how much of these vegetables you would need to obtain the same amount of calcium than you would in a glass of milk. They bio-availability is the percentage of a certain nutrient that you body is capable of absorbing.  

The relative bio-availability of calcium is higher in broccoli (61%), bok choy (54%) and kale (49%) than in milk (32%); however in other vegetables like spinach or in sweet potato is lower (22%). As the vegetables have less amount of calcium, we would need around 400gr of broccoli, 130gr of cok choy, 100gr of kale 1.8 kg of spinach or almost 1kf of sweet potato. 

Some have suggested basil as a good source of calcium. 2 tablespoons of dry basil (30gr) provide us with 592mg of calcium (3), which is a really good amount! 250ml of milk gives us only 330mg! However, can we realistically have 2 tablespoons of basil per day? Is that sustainable? I mean, how much is a glass of milk? a few pennies? What about a jar of dry basil? At least 1.5 pounds? Could you have two little spice jars per day? 


Let's get on with the links between osteoporosis and calcium intake. 

PEN has a brilliant article about it here (link) and I really recommend you read it if you are subscribed. I have tried to summarised it as best as I could.

Many of the arguments about this topic are based on observational studies. These showed that those countries with higher intakes of calcium have higher rates of osteoporosis. However, we know that observational studies are not very reliable to establish conclusions and even less to make recommendations on a population level, don't we? This is the classic problem of confusing an association with a cause. 

Despite there were higher rates of hip fracture in developed countries where the intake of calcium was higher, this was due to the mistake of making the comparison with Asian countries, were the intake is lower but the activity levels are much higher. When studies take into account the differences in manual labour, those countries that are highly urbanised and sedentary have similar hip fractures to the United States (7).

Calcium intake is a very important factor for bone health BUT physical activity is more important (8). When we don't take into account the activity factor when comparing countries, the results cannot be understood properly. In other words, comparing a country that has a predominantly sedentary work force to a country that has a largely manual work force does not provide reliable results, especially if you are looking at an outcome that is greatly effected by physical activity, such as hip fractures.

This lack of control of an important variable is a common problem in observational studies, especially when the unit of comparison is by country and not by participants in the research. This problem is called an ecological fallacy.

Lactose intolerance

There are people who suffer from lactose intolerance: the enzyme needed to digest lactose (lactase) is in a very small amount and the intake of dairy products causes gastrointestinal discomfort (gas, diarrhoea, bloating). For this group it is recommended to reduce the intake of dairy to a tolerable level.

James Palinsad via Flickr

Evidence shows that even those who are diagnosed with lactose intolerance can tolerate one cup of normal milk (12 grams of lactose) or dairy products with lower lactose such as yogurt and cheese (9). Lactose tolerance improves when consumed as part of a meal, perhaps because of slower gastric emptying (9), and it has also been found that the consumption of small amounts of lactose facilitates the adaptation of lactase and a reduction of the symptoms of lactose intolerance (9, 10).

Last but not least, my favourite: the consumption of low fat products make you eat more, because it does not fill you up as much and because when it is light, you feel like you can eat more of other stuff. 

Let's see. First, the fat we found in the milk is saturated; it would be better for you to have a glass of skimmed milk and a toast with avocado, whose fat is unsaturated and good for your heart. And that other stuff about " I have eaten a low fat yogurt, which is light and good, so I am gonna have a muffin" depends of the individual's mind set... and can be applicable to anything in life. If you think that having a low fat product allows you to eat a muffin, after you go to the gym you will probably think you deserve a bag of chips and if you take the stairs you will have a piece of cake when you get to your office. 

I do not think it is responsible to recommend at a population level to chose full fat dairy, especially when we do have low fat alternatives. And just in case we want to justify that recommendation by talking about the lack of fat soluble vitamins in the skimmed milk, keep in mind that the avocado and toast I was suggesting before will provide you with 146UI in a 100gr, whereas 100gr of milk will give you 102 UI.  


Message to take home

We are neither pro nor anti dairy, we just wanted to clarify what the current evidence is actually telling us.

If you drink milk and eat dairy produce and have no problems then continue to do so. 

If it doesn't agree with you, try with yogurt or cheeses. Dairy is an excellent easy source of calcium. If you have options, choose low fat and low sugar. 

If you don't like dairy or it makes you sick, try calcium fortified vegetable drinks (with no sugar, please!), vegetables rich in calcium, tofu, nuts and linseed or sesame seeds. 

Referencias
1. Dietitians of Canada. How much calcium is absorbed from calcium-enriched foods and beverages, such as orange juice, soy and rice beverages, and tofu made with calcium and unfortified plant foods? In: Practice-based Evidence in Nutrition [PEN]. 2012 March 11 [cited 2015 May 14]. Available from:/KnowledgePathway.aspx?kpid=16524&pqcatid=144&pqid=19160&kppid=19162&book=Evidence#Evidence. Access only by subscription or sign up for a free two-week trial.
2. Weaver CM, Proulx WR, Heaney R. Choices for achieving adequate dietary calcium with a vegetarian diet. Am J Clin Nutr. 1999 Sep;70(3 Suppl):543S-8S. Abstract available from:https://www.ncbi.nlm.nih.gov/pubmed/10479229.
3. http://nutritiondata.self.com/facts/spices-and-herbs/173/2

4. Tognolini M, Barocelli E, Ballabeni V, Bruni R, Bianchi A, Chiavarini M, et al. Comparative screening of plant essential oils: phenylpropanoid moiety as basic core for antiplatelet activity. Life Sci. 2006 Feb 23;78(13):1419-32. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/16274702.

5. Amrani S, Harnafi H, Gadi D, Mekhfi H, Legssyer A, Aziz M, et al. Vasorelaxant and anti-platelet aggregation effects of aqueous Ocimum basilicum extract. J Ethnopharmacol. 2009 Aug 17;125(1):157-62. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/19505553.

6. Umar A, Imam G, Yimin W, Kerim P, Tohti I, Berké B, et al. Antihypertensive effects of Ocimum basilicum L. (OBL) on blood pressure in renovascular hypertensive rats. Hypertens Res. 2010 Jul;33(7):727-30. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/20448636.

7. Lau EM, Lee JK, Suriwongpaisal P, Saw SM, Das De S, Khir A, et al. The incidence of hip fracture in four Asian countries: the Asian Osteoporosis Study. Osteoporos Int. 2001;12(3):239-43. Abstract available from:https://www.ncbi.nlm.nih.gov/pubmed/11315243.

8. Pripp AH, Dahl OE. The population attributable risk of nutrition and lifestyle on hip fractures. Hip Int. 2015 Apr 23. doi: 10.5301/hipint.5000229. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/25907388.
9.Dietitians of Canada. What dietary factors affect lactose tolerance? In: Practice-based Evidence in Nutrition [PEN]. 2008 April 22 [cited 2015 May 14]. Available from /KnowledgePathway.aspx?kpid=1820&pqcatid=146&pqid=&kppid=3476&book=Evidence#Evidence. Access only by subscription or sign up for a free two-week trial.

10. Hertzler SR, Savaiano DA. Colonic adaptation to daily lactose feeding in lactose maldigesters reduces lactose intolerance. Am J Clin Nutr. 1996;64:232-6. Abstract available from:https://www.ncbi.nlm.nih.gov/pubmed/8694025