Fitness professionals know all too well how fervently their clients are looking for a magic pill that will help them shed pounds and reduce unwanted body fat. Now it appears that something as simple as increasing daily intake of dietary calcium may represent a new way of combating the obesity epidemic. In fact, more and more research studies are uncovering a strong link between calories and calcium stores in the body.
This article examines the research on the association between calcium and fat storage and describes the mechanisms by which dietary calcium may influence obesity. It also explains calcium’s contribution to other health outcomes and provides practical suggestions for selecting healthy foods with a high calcium content.
The link between calcium and obesity was discovered by accident more than 15 years ago as researchers were examining the role of calcium in regulating blood pressure. At the end of the study period, scientists noticed that the subjects who had increased their dietary calcium intake were showing decreases not only in blood pressure but also in body fat (Zemel et al. 2000). At the time, this finding was considered a random occurrence because there was no known connection between calcium intake and body fat.
Years later, a team of scientists studying obese mice discovered that high levels of intracellular calcium allowed accumulation of increased fat in adipose cells (Zemel et al. 2000). Then another study found that high levels of intracellular calcium increased fat in human adipose cells (Shi et al. 1999). Ultimately, researchers from the University of Tennessee compared these new findings with the older findings and launched additional research on how dietary calcium might influence obesity through its effect on energy balance (Zemel et al. 2000).
Scientists had also known for many years that increasing calcium consumption lowers the amount of circulating vitamin D that is activated by the body. (In fact, the only time the body needs to activate vitamin D is when blood levels of calcium fall too low.)
Then, in 2001, researchers discovered that active vitamin D opens a calcium channel on the outer membrane of human fat cells, allowing calcium to pour into the cells in response to low dietary calcium intake (Shi et al. 2001).
All of these studies led to the knowledge that high internal concentrations of calcium
- stimulate the fat cells to increase fat synthesis;
- increase the enzymes that help produce fat;
- decrease fat breakdown.
Once these observations linking calcium and obesity were published, other investigators began to reanalyze findings from previous clinical trials on dietary calcium and bone health to see if the older data supported the link with obesity. Sure enough, higher dietary calcium intakes were consistently associated with a lower risk of being overweight (Davies et al. 2000).
A more recent study also found an association between high dietary calcium and low body weight, low fat mass and low abdominal obesity (Loos et al. 2004). This echoed the findings of an Australian study, which demonstrated that high calcium intake was significantly related to lower body mass index (BMI) and other indicators of general obesity in adults (Soares, Binns & Lester 2004). Finally, a longitudinal study of children from 2 months to 8 years old correlated high dietary calcium intakes with low percentages of body fat (Skinner et al. 2003). In all these studies, higher dietary calcium was consistently associated with lower indicators of obesity, supporting the concept that energy balance may be regulated in part by calcium intake.
Calcium is by no means the only factor scientists associate with obesity. In fact, one study estimated that dietary calcium accounted for only about 3% of the variation in body weight in the subjects they analyzed (Davies et al. 2000). Other researchers have estimated the portion to be no higher than 10% (Heaney 2003; Skinner et al. 2003). Moreover, it appears that high calcium intake predicts lower body weight and fat mass only when study subjects consume fewer calories than control subjects (Teegarden 2003). That said, more and more evidence suggests that calcium intake plays an important role in preventing obesity and promoting weight loss during energy restriction.
There are several reasons why it may be particularly important for our clients to consume adequate calcium when trying to lose weight. Studies have shown that calcium can
- enhance weight loss;
- meet increased absorption needs when dieting;
- regulate energy intake and decrease fat absorption.
Although it is not known why dairy products led to greater fat loss in these subjects, animal studies have also shown that high dairy intake is more beneficial for fat loss than a similar level of calcium provided by supplements (Zemel et al. 2000). One theory is that increased fat loss might be related to increased fat oxidation when people are on a high calcium diet. A study of healthy, normal-weight adults found that more fat was burned by subjects who consumed high amounts of calcium than by those who ate less calcium (Melanson et al. 2003).
Meet Calcium Needs When Dieting. Another possibility that researchers are exploring is that calcium absorption is hindered when subjects are dieting. In one study, women who consumed 1,200 mg of calcium daily and lost weight while on a restricted diet had significantly lower total calcium absorption than women who were maintaining their weight (Cifuentes et al. 2004). More importantly, the amount of calcium absorbed did not meet daily absorption requirements. This led the researchers to suggest that whenever calories are restricted in older women, daily calcium intake should be increased to prevent bone loss. Because the focus of this particular study was on how much calcium postmenopausal women needed to absorb to prevent bone loss, it is not clear if these findings extend to men and younger women. However, animal studies have shown that both young and old subjects absorb less calcium whenever calories are restricted. So it is quite possible that future research may show that adequate calcium intake is positively linked to sustained weight loss and that insufficient calcium absorption somehow contributes to weight loss plateaus.
Regulate Energy Intake and Decrease Fat Absorption. Two other mechanisms have been proposed to explain the link between calcium and energy balance. The first hypothesis is that calcium may alter energy intake. This came from a study that compared the effect of a high- versus a low-dairy-calcium breakfast (identical in calories) on satiety and subsequent food choices (Ping-Delfos, Soares & Cummings 2004). Subjects who ate the high-dairy-calcium breakfast spontaneously consumed significantly less food over the next 24 hours than those who ate the other breakfast. The second hypothesis is that calcium may alter energy absorption from the gut. Some studies suggest that dietary calcium may decrease fat absorption and therefore lower relative energy intake by preventing the absorption of free fatty acids (Denke, Fox & Schulte 1993; Welberg et al. 1994).
Several studies have shown that calcium consumed in foods—particularly dairy foods—contributes to weight loss and prevents weight gain to a greater extent than calcium derived from supplements. This may be because dairy products contain many other bioactive components in addition to calcium. Two of these components, branched-chain amino acids and angiotensin-converting enzyme (ACE) inhibiting compounds, are thought to augment the effects of calcium in preventing obesity (Zemel et al. 2004). Some evidence suggests that the high levels of these branched-chain amino acids—especially leucine—in milk may increase protein synthesis and therefore funnel dietary energy away from adipose tissue and toward muscle. There is also evidence that ACE inhibition decreases both fat synthesis and body weight in mice. Similarly, hypertensive patients who take prescription ACE inhibitors to reduce blood pressure may lose a little weight as a side effect of the medication. Because dairy products contain so many unexplored bioactive compounds, it is likely that other possible mechanisms will be found through further research. For the time being, however, we have only the observation that dairy products are often more helpful with weight loss than calcium supplements.
Remind clients that it is possible to get too much of a good thing when it comes to calcium. Although adequate calcium intake is health protective, excessive amounts of this mineral are associated with a higher incidence of kidney stones and impaired kidney function. Too much calcium can also interfere with the absorption of other important minerals, such as iron, zinc, magnesium and potassium. For these reasons, it is advised that people consume no more than 2,500 mg per day, the recommended Upper Intake Level for calcium (Food & Nutrition Board [FNB] 1997).
So, what does all this research bode for clients wanting to lose a few pounds or to prevent weight gain? First, they need to understand that calcium is not a magic bullet. Inform them that dietary calcium accounts for only 3%–10% of the differences in body fat noted in the research. Also remind clients that consuming enough calcium is important for many health-related reasons other than weight loss (see “Functions of Calcium” on page 50).
In all likelihood, most of your clients consume too little calcium on a daily basis. On average, Americans get 742 mg per day, compared to the recommended Adequate Intake of 1,000 mg per day for adults under 50 years old or the 1,200 mg per day for those over age 50 (FNB 1997). That’s why it is also vital to make clients aware of good sources of dietary calcium. People who eat all foods (omnivores) and vegetarians who consume dairy products (lactovegetarians) will have an easier time incorporating sufficient calcium into their diets than people who eat only plant products (vegans).
One dairy food paradox to bring to your clients’ attention is that cottage cheese is often included in traditional weight loss diets. Although a half-cup serving of nonfat cottage cheese does provide an excellent supply of protein (20 grams) for few calories (96 calories), it contains a lowly 36 mg of calcium. That’s because most of the calcium is removed from the curd during processing. (With other cheeses, the opposite is true: Calcium becomes part of the curd during processing.) For a look at higher-calcium cheese choices for dieters, see “Calcium-Rich Foods” on page 51.
Mopping Up Milk Myths
One major hurdle in getting clients to increase their dairy intake is that there are long-standing myths associated with milk consumption. The most prevalent myth is that drinking milk increases mucus production. However, there are no data in the scientific literature to support any relationship between milk consumption and mucus production (Lee & Dozor 2004).
In the late 1980s, some research suggested that lactose in milk was associated with ovarian cancer, but subsequent studies have shown very mixed results. Most studies have found no overall association between milk consumption and ovarian cancer.
Another myth is that lactose-intolerant individuals cannot consume any dairy products. Actually, lactose intolerance varies quite a bit among individuals, and many can drink up to a cup of milk per day with meals without experiencing uncomfortable symptoms. Yogurts contain less lactose than comparable quantities of milk, owing to bacterial action during the production of yogurt. Cheeses have very little lactose because it is depleted by bacteria during the extended curing process. For those with severe lactose intolerance, there are lactose-free milks available that retain the full complement of calcium.
The bottom line is that the majority of data do not consistently support any negative consequences from consuming low-fat or nonfat dairy products. In fact, quite the opposite is true: There are substantial data to support positive outcomes, including better bone mineralization, lower blood pressure, lower risk of colon cancer and lower risk of obesity.
Vegans can get substantial calcium in their diets by regularly consuming legumes and vegetables that are naturally high in calcium. Although the foods listed in “Calcium-Rich Foods” on page 51 contain the highest calcium per usual serving for their class (e.g., almonds have more calcium than other nuts, while oranges have more than other fresh fruits), remember that all foods contain some calcium. Two examples: A cup of cooked oatmeal contains 19 mg of calcium, and a 3-ounce chicken breast contains 12 mg.
Still, not all foods are equal when it comes to calcium absorption. High levels of natural food components like oxalates (found in spinach, sweet potatoes, rhubarb and beans) and phytates (found in seeds, nuts and grains) can prevent calcium absorption in the gut. In general, calcium is best absorbed from low-oxalate vegetables like bok choy and broccoli. To optimize their calcium intake, some vegans may want to consider calcium-fortified foods or calcium supplements, especially if they are consuming less food than usual because they want to lose weight.
Yet another way to help clients lose weight by incorporating calcium in their diets is to make them aware of nutrient density (i.e., how much calcium is available per calorie of the food). The best natural food for calcium density is bok choy, with okra and skim milk following close behind. Most natural cheeses, artificially sweetened yogurt, 2% and whole milk, kale, broccoli and green beans all provide 1.5–3 mg of calcium per calorie. These are foods that can easily be incorporated into meals to promote calcium intake while still keeping total dietary calories low.
Here are some practical ways that clients following a lower- calorie diet can readily incorporate calcium-dense foods into meals:
Breakfast. Fortified cereals and soymilk give vegans a healthy way to start the day with substantial calcium. For example, a cup of Total® cereal with a half cup of milk provides almost 1,000 mg of calcium. However, clients should read food labels, as not all fortified cereals are fortified with calcium and some may have calcium levels as low as 10 mg per serving. Adding an ounce of nuts to cooked oatmeal or your favorite dry cereal will increase the calcium level by 20–75 mg (over and above any calcium in the milk or soymilk used to moisten the cereal). Smoothies made with skim milk, fortified soymilk or fortified orange juice are a quick and easy way to get another 150–300 mg of calcium (per cup of milk or juice used).
Lunch. A cup of skim-milk yogurt or fortified soy yogurt that is artificially sweetened provides around 300 mg of calcium for less than 200 calories. Simply topping a salad with an ounce of cheddar or blue cheese or a quarter cup of tofu will increase calcium intake by 200 mg for about 100 calories. (But note that the tofu must be processed with calcium as opposed to magnesium!) Milk-based soups like clam chowder or vegan corn chowder are tasty ways to include milk or fortified soymilk in a hot lunch.
Dinner. Sprinkling cheese on a casserole is a quick and easy way to add 200 mg of calcium per serving of the dish. Including shredded bok choy or chopped broccoli in highly seasoned foods, like lasagna, soups and stir-fries, is another option. Black beans can be served with rice, added to mar- inated bean and corn salads, or puréed and topped with a spoonful of plain yogurt and chopped green onion for a wonderful calcium-rich soup. In many recipes plain yogurt can replace sour cream with a minimal change in flavor. Substituting a cup of plain skim-milk yogurt (488 mg of calcium, 137 calories) for a cup of sour cream (267 mg of calcium, 492 calories) adds nutrients and subtracts calories from casseroles, quiches, salad dressings and dips. Puddings or custards made with skim milk add calcium to desserts. A half cup of chocolate ice milk has 94 mg of calcium and 95 calories. And assorted cheeses and fruits make a traditional—and beautiful—French dessert.
Snacks. For those who eat dairy products, string cheese comes in individually wrapped 1-ounce portions that provide 200 mg of calcium for only 80 calories. Eaten with an apple (another 80 calories), this makes a healthy and satisfying snack for less than 200 calories. A handful of almonds, suitable for both vegans and omnivores, provides 75 mg of calcium for 169 calories and is easy to carry. Another great snack option is a quarter cup of dry-roasted soy nuts (60 mg of calcium; 194 calories). Dipping raw veggies (including broccoli) in low-fat yogurt seasoned with dry onion soup mix is a great high-calcium, low-calorie snack to serve when friends come to visit.
Beverages. An excellent way to increase calcium in the diet is to swap sugar-sweetened carbonated beverages for milk. One cup of soda contains 104 calories but only 7 mg of calcium, whereas the same quantity of nonfat milk has 90 calories and 300 mg of calcium. Even those who crave a sweet beverage can get their fix by eschewing soda and opting for a cup of nonfat chocolate milk, which contains a measly 144 calories but boasts 292 mg of calcium.
Cheers for Calcium
Increasing dietary calcium may be just the edge your clients need to optimize lifestyle changes that will result in healthy weight loss. Continued consumption may also complement exercise and moderate calorie intake to help clients maintain lean body mass and a healthy body weight once they reach their own individual target.