Calcium intake spinach

Calcium contents of whole rats were determined at the end of the experiment. Weight gains and calcium retentions were better when the animals were fed tomatoes than when they were fed spinach, even though the calcium intake on the higher level of spinach was about 20 times greater than when tomatoes were fed. 

Figure 1. Calcium intake and excretion of older rats (63 days) and younger rats (33 days) on a low fiber diet (1), raw spinach (2), cooked spinach (3), filter paper (4), and high filter paper (5). Dietary intake is indicated by the top of the bar. Balance is indicated by the bottom of the bar. Adapted from Ref. 12.

In two women studied by Fincke and Garrison (28), the calcium of kale was better utilized than that of spinach, when the vegetables supplied 80-86% of the calcium in the diet. One diet contained kale and two diets contained spinach (about 500 g) calcium intakes were 400, 304, and 445 mg/day, respectively. Two 3-day balances were determined after 3 days on each diet. Calcium balances were negative on all diets, but were more negative when the spinach was consumed. 

Bricker et al. (30) reported that there were no statistically significant differences between the calcium balances of eight women on cocoa and non-cocoa diets. The women were studied for three to seven 4-day periods. Calcium intake was 670 mg/day with the addition of milk and 679 and 755 mg/day with the addition of milk and cocoa. Five levels of cocoa, supplying from 5.6-52.6 g/day, were tested. These amounts would likely contain from 25-280 mg of oxalic acid, which was not nearly as much as was added when spinach was fed. With the inclusion of cocoa in the diet, the urinary calcium fell and fecal calcium rose. There were also increases in the fecal excretion of dry matter and nitrogen. 

In the studies on humans there appeared to be decreased calcium balances when 200 g or more of spinach per day was included in the diet. In two of the studies in which women were fed spinach, calcium intakes were below the Recommended Dietary Allowance of 800 mg/day (37). Some studies were conducted for short period of a week or less, which may not be sufficient time to adjust to a change in diet. From measurement of calcium excretion in urine after a test meal, it was shown that the calcium in oxalate-containing vegetables was less well-absorbed than that of milk or of vegetables not containing oxalic acid. However, this would not necessarily affect calcium balance, since the total amount of calcium in the diet would have to be considered. The effect of a combination of oxalic acid and fiber on calcium bioavailability should be further investigated. 

Review of studies on the effect of oxalic acid on calcium bioavailability in rats and in humans indicates that most of the research was done between 1930 and 1950. Decreased availability of calcium in young rats was reported when spinach containing oxalic acid was fed with low calcium diets. The extent of the effect of oxalic acid on calcium availability was shown to be related to levels of calcium and oxalic acid, as well as the presence of vitamin D in the diet. In human studies there was generally no effect of oxalic acid on calcium balance however, in a few studies decreased calcium balances were reported. There is recent evidence that oxalic acid consumed along with a moderately high level of fiber intake may have adverse effects on calcium balance of human subjects. 

Spiers (18) reported that the feeding of 14% dried New England spinach in the diet resulted in decreased growth and less calcium retention, as determined by body calcium content (Figure 3). Rats 28 days old were fed until 60 days of age. All diets contained about 0.3% calcium, and in the control diet practically all of the calcium was from skim milk. In the other diets, one-half of the skim milk was replaced by turnip greens, tendergreens, collards, kale, or New Zealand spinach to furnish an equal amount of calcium. Spinach was the only one of the greens fed which contained considerable oxalic acid. The calcium of the spinach appeared not only to be utilized poorly, but spinach also impaired utilization of the milk calcium. Food intake of the rats on the spinach diet was also lower. 

Calcium Acetate (PhosLo) [Calcium Supplement/ Anti arrhythmic/Mmeral/ Electrolyte] Uses ESRD-associated hyper-phos-phatemia Action Ca " supl w/o aluminum to X P04 absorption Dose 2-4 tabs PO w/ meals Caution [C, ] Contra t Ca Disp Gelcap SE Can t Ca, hypophosphatemia, constipation Interactions t Effects OF quinidine X effects W/ large intake of dietary fiber, spinach, rhubarb X effects OF atenolol, CCB, etidronate, tetracyclines, fluoroquinolones, phenytoin, Fe salts, thyroid hormones EMS Pts have reduced renal Fxn, monitor ECG for signs of electrolyte disturbances OD S/Sxs of hypercalcemia (confusion, weakness, GI upset, constipation, N, V, and cardiac arrhythmias) give IV fluid for diuresis symptomatic and supportive Calcium Carbonate (TumS/ Alka Mints) [Antacid/ Calcium Supplement/Mineral/ Electrolyte] [OTC] Uses Hyperacidity associated w/ peptic ulcer Dz, hiatal hernia, etc Action Neutralizes gastric acid Dose 500 mg—2 g PO PRN -1- in renal impair Caution [C, ] Disp Chew tabs, susp SE t -1- PO constipation Interactions X Effect OF tetracyclines, fluo-... 

Management. Recurrent stone-formers should maintain a urine output exceeding 2.51/d. Some benefit from restricting dietary calcium or reducing the intake of oxalate-rich foods (rhubarb, spinach, tea, chocolate, peanuts). 

Spinach and rhubarb contain oxalic acid (Table 14.7). Individuals prone to kidney stones composed of highly insoluble calcium oxalate must limit their intake of foods containing oxalic acid. 

Absorption of calcium may be prevented by the formation of insoluble calcium oxalate where oxalic acid forms a significant proportion of intake. The most notable example is spinach which contains sufficient oxalic acid to render all its calcuim non-available with some to spare for other calcium present in the diet. There is some doubt, however, that this factor has any major effect upon nutrition in normal circumstances. 

Oxalates—Nutritionists have long been concerned about whether oxalates, which are present in such foods as rhubarb and spinach, might bind with sufficient amounts of calcium and/or iron so as to produce deficiencies of these minerals. However, experiments have shown that such effects are not likely to occur in man unless (1) the mineral intake is marginal and (2) unusually large amounts of these foods are eaten, along with other sources of oxalates like almonds, beet greens, cashew nuts, cocoa, or tea. ... 

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