Why to head for the greens!

I’ve been exploring various sources of calcium and seeing how they stack up against one another. In general, cheese, with its low water content, does well in the Most Calcium per Gram category, especially Parmesan cheese. Leafy greens do rather well with Most Calcium per Calorie – collard greens and Chinese cabbages are winners here.

So why pick leafy greens over dairy products? Besides side-stepping the protein issue, leafy greens have so much going for them that I’m ashamed that I don’t eat them at every meal. Let’s compare a cup of plain low-fat yogurt with a cup of cooked collard greens on a smattering of nutrients: fiber, fat-soluble vitamins, and a few minerals.

Plain low-fat yogurt vs.Cooked collard greens

	Yogurt	Collard Greens
Fiber:	0g	5g
Vitamin A:	125 IU	15416 IU
Vitamin D:	n/a	n/a
Vitamin E:	0.1 mg	1.7 mg
Vitamin K:	0.5 mcg	836 mcg
Calcium:	448 mg	266 mg
Iron:	0.2 mg	2.2 mg
Magnesium:	41.7 mg	38.0 mg
Phosphorus:	353 mg	57.0 mg
Potassium:	573 mg	220 mg
Sodium:	171 mg	30 mg

Collard greens clearly have the upper hand when it comes to fiber and fat-soluble vitamins (water-soluble vitamins – C and the Bs – are more of a mixed bag), but yogurt comes rushing back in the mineral department, with the exception of iron.

But more sodium is not necessarily better, despite what Cargill might tell you, and too much phosphorus in conjunction with too little calcium is bad news for your bones.

Two more points I’d like to bring out. First, yogurt has 32 mg of omega-3 fatty acids and 76 mg of omega-6 (~1:2.4 ratio) compared to collard greens’ 177 mg and 133 mg, respectively. That’s a 1.3:1 ration, which is great! The more omega-3’s, the better, especially when they outnumber omega-6’s.

Second, a cup of collard greens has a third of the calories of a cup yogurt, so you could eat three times as much and get the upper hand on the minerals! I would recommend, however, adding between a quarter of a teaspoon to a teaspoon of olive oil or butter per cup of greens. Doing so would add up to 40 more calories, but also increase absorption of fat-soluble vitamins, satiety, and deliciousness.

I could go on about phytonutrients and the Brassica family, but I believe I hear the greens of a farmers’ market calling my name.

Photo by Mark Farnham

Calcium and protein: friends or foes?

In the last post, we saw that dairy products are a fine source of calcium, thanks to the absorption-enhancing property of lactose and the density of calcium by weight or calorie. So why consider anything else? I think many people have an idea that protein, in which dairy products are rich, interferes with calcium or bone health in some way. In the chapter on bone health in Krause’s Food and Nutrition Therapy, John JB Anderson states that “the relationship between protein and calcium is unsettled” (625).

Let’s take a step back. What is this relationship? On the one hand, protein is considered to have an anabolic (building) effect on bone. After all, around 25% of the bone matrix is protein in the form of collagen fibers. Calcium and phosphorus make up the hydroxyapatite that gives bone its rigidity. On the other hand, a chronically low intake of protein decreases the serum concentration of albumin, a protein that transports nearly everything in the blood, including calcium (Anderson, 625).

So why would high protein intake pose a problem? Here’s where the textbook gets a little fuzzy. First it says that “actions of proteins and their absorbed amino acids… [have] a catabolic [breaking down] effect resulting from the generation of an acid load” (625). But as far as I can tell, extracellular excesses of acid are buffered primarily by bicarbonate - calcium doesn’t have much to do with it.

The second reason given is that urinary losses of calcium increase following meals that contain large amounts of animal protein (625). The exact mechanism is not clear, but it may be because the sulfates generated by the metabolism of sulfur-containing amino acids (cysteine, cystine, methionine) bind to calcium ions in the kidney and prevent them from being reabsorbed (Gallagher, 115). A list of food sources of sulfur follows: meat, poultry, fish, eggs, dried beans, broccoli, and cauliflower. This is a bit misleading, as 3 oz of beef has fourteen times as much methionine as 1 cup of cooked broccoli.

Studies tracking protein consumption and bone fractures or bone mineral density are… numerous. Some come out in favor, some come out a wash. I would say that most people should consider getting more calcium from vegetables, and in the next post, I’ll explain why it’s a great idea.

Photo source: fooducate.com

Can we use calcium from dairy products?

A few weeks ago when I entered Aunt Gayle’s hospice room, the gathered family had a nutrition question for me: can humans absorb the calcium found in milk and other dairy products? I was fairly confident that dairy is a good source of calcium and is well absorbed. If not, the government and the dairy industry’s been doing us a huge disservice for decades.

Then my mother-in-law raised the same question this weekend. Her doctor had recommended leafy greens as a calcium source. Again, I was fairly confident that most leafy greens are a good source of calcium, though not necessarily as well absorbed.

So what's the deal? Should one consume dairy products for the calcium? My newly purchased textbook, Krause’s Food and Nutrition Therapy, by L. Kathleen Mahan and Sylvia Escott-Stump (Saunders-Elsevier, 2008), offers two reasons to do so. First, dairy products are the most concentrated calcium sources, and second, lactose enhances calcium absorption, probably even in those with lactose intolerance (104, 106).

A cursory glance at a Google Scholar search related to lactose-enhanced calcium absorption reassured me that this reason was probably valid.And while "most concentrated" sounded about right, I was curious as to how exactly that played out.

I started calculating the concentration of calcium in some foods, both dairy and non-dairy to get some numbers. I began by calculating milligrams of calcium per calorie, but that didn’t result in dairy being uniformly more concentrated:

Food	Calcium (mg)	Kcals	Mg Ca per kcal
Yogurt, plain, low fat, 1 cup (245g)	448	154	2.9
Milk, 2%, 1 cup (144g)	286	122	2.3
Cheddar cheese, 1 oz (28g)	202	113	1.8
¼ block firm tofu (81g)	163	57	2.9
Kale, 1 cup cooked (130g)	94	36	2.6
Broccoli, 1 cup cooked (156g)	62	54	1.2
Almonds, 1 oz (28g)	75	169	0.4

Tofu stands eye-to-eye with yogurt, a cup of kale beats a cup of milk - what's going on? I switched to milligrams of calcium per gram, which still didn’t yield the results I expected:

Food	Mg Ca per gram
Cheddar cheese, 1 oz	7.2
Yogurt, plain, low fat, 8 oz	1.8
Milk, 2%, 1 cup	1.2
Almonds, 1 oz	2.7
¼ block firm tofu	2.0
Kale, 1 cup cooked	0.7
Broccoli, 1 cup cooked	0.4

Here, water content plays a big role - generally the more water, the heavier the food is. Cheddar is the leader by far, since cheese is basically milk wrung of water. This time, almonds are doing pretty well, and tofu is still a champ. NOTE: These calculations are based on calcium-set tofu, not the silken type, which has about 80% less calcium. Straight-up cooked soybeans have about 0.6 mg Ca per kcal, and 1.0 mg per gram.

Bottom line – the author of the statement "Cow's milk is and dairy products are the most concentrated sources of calcium" has a different understanding of “concentrated sources” than I do.

Next up: the relationship between protein and calcium.

Photo Source: UMN Extension