Calcium’s Role in Weight Loss in Adults
A Positional Essay for the General Public
Carina Sorenson
Fall 2005
A paper for TIME Magazine
Introduction
The National Dairy Council has recently introduced their 3-A-Day campaign to lose weight, and printed it on their products. Their claim is that consumption of “three servings of dairy a day in a reduced-calorie diet supports weight loss”. Is the National Dairy Council campaign’s purpose to help people lose weight, or to increase sales? If any company can campaign in such a way to encourage people to lose weight and increase their sales at the same time, it can be a win-win situation. However, if companies base their data on a few studies, and do not have significant sources, then the public is being misled. A few studies have found that with caloric restriction, combined with calcium intake participants lose more weight compared to caloric restriction without calcium supplementation. Many other studies have concluded that calcium does not affect amount of weight loss. This conflicting data leads to further questioning. How can studies find completely conflicting results? By analyzing studies supporting the 3-A-Day campaign, and comparing their results to studies that contradict these findings, I will attempt to draw a more concrete, less controversial conclusion. I will be considering calcium intake, both supplemental and dietary (dairy product consumption), population, and any other diet restrictions to find a more definitive conclusion. Can the RDA recommendation of 1000 mg of calcium play a significant role in amount of weight loss independent of a 500-calorie deficit? Because I have analyzed numerous studies, I believe that calcium does not increase weight loss.
I will be analyzing and comparing five studies of human intake of calcium and weight loss, three studies of rats and mice with calcium-rich diets and body weight, and four reviews which overview a few studies to show a relationship between calcium and weight loss. These studies and reviews span over the years from 2000-2005. These studies and reviews discuss the possible benefits of calcium taken as a supplement or through dietary intake.
Calcium is administered in a pill form in most cases, as many vitamins are packaged, although other forms exist. Calcium is increased in a diet by including dairy products with a serving size of calcium of 300 mg or 30% of the daily values determined and supported by government standards. The role of calcium is measured by the direct correlation of change in body weight, adiposity (defined as animal fat), and fat mass.
Most studies included a wide range of subjects classified as adults. Three studies specifically studied male Wistar rats, and another studied female C57BL/6J mice or Sprague Dawley rats. A few studies were more specific about the human population studied and their subjects were obese African-American adults or pre-menopausal and post-menopausal women.
Three of the five studies of adults found that calcium did not increase weight loss. Of the three studies on rats and mice, two found that calcium regulates adiposity, which is animal fat. Three of the four reviews concluded that calcium does significantly affect weight loss. A few studies were supported by National Institutes of Health Grants (Shapses, 2004). One scientist, Michael B. Zemel, has produced numerous studies of calcium and obesity, and many of his studies are supported, and often times funded by, the National Dairy Council. Additionally, Michael B. Zemel has served on speaker panels for the National Dairy Council. Zemel et al. studied both obese adults, and more specifically African- American adults. Factors, such as funding, may influence the science of such studies.
The Issue of Weight
Obesity has recently become a recognized problem in the United States. With over 60% of the United States’ population being overweight or obese, it is impossible to ignore. Half of these adults are considered overweight according to calculations which involve height to weight ratios known as a Body Mass Index (BMI) of units kg/m2. The exact calculation includes a conversion of weight in pounds to kilograms. Height is converted from feet and inches to meters. BMI is calculated as weight in kilograms divided by height in meters squared. The BMI is a very rough estimate of a persons’ health compared nationally. Adults with a BMI between 26-30 kg/m2 are considered overweight, while anyone with a BMI over 30 kg/m2 is considered obese. Obesity increases many health risks.
With a BMI higher than 30 kg/m2, statistics show increased mortality, increased risk of cardiovascular disease (CVD), type 2 diabetes, osteoarthritis, and some cancers. Americans are encouraged to diet and exercise; however, this requirement for a healthy, happier life can be grueling, and has high drop out rates. Weight loss often leads not only to fat loss but also fluid loss, bone loss, and muscle loss. Rapid fluid loss occurs when eliminating carbohydrates. Fast results of pounds lost are easy to read on a scale. However, the fluid loss may easily lead to dehydration, and hinder other normal bodily functions. Bone and muscle loss with extreme dieting may eventually lead to osteoporosis and bone fractures. The elderly population in particular has increased potential of bone loss. Decreasing the growing obesity rates are crucial, but an understanding how to diet safely is important as well.
Calcium increases weight loss
A few recent studies have shown that a minimal reduction of 500 calories per day, combined with 800-1400 mg of calcium intake (either in supplemental form or in dietary sources) resulted in weight loss, fat loss, and a decrease in trunk fat (area of waistline). These studies observed a significant weight loss with additional calcium compared to caloric restriction without calcium. An additional positive effect of increasing calcium intake while dieting is that while losing weight, the loss of bone and muscle decreases because calcium increases bone growth and strength (Ilich, 2005).
Some scientists have proposed ideas about calcium’s impact on fat cell growth, storage, and excretion. Calcium works within the cell to impact the creation and growth of fat molecules. With higher intakes of calcium, a change of charged calcium molecules in the adipocytes (fat cells) suppresses a hormone response. Because the calcium cannot stop the hormone response, increased fat storage occurs. Calcium may also be helpful by binding to fatty acids in the digestive system which decreases the amount of undigested fat absorbed and increases the amount of fat excreted through the bowels. This is the mechanism by which increased calcium intake may increase weight loss. However, too many studies have found conflicting results (Ilich, 2005).
Calcium was initially studied to analyze the effects of bone mass or blood pressure. Recent reviews have re-analyzed these past studies to find the surprising, and often times overlooked result of increased weight loss of individuals with increased calcium consumption. These studies would simultaneously restrict calories, so the study subjects would lose weight more rapidly. When the groups were compared, the higher the calcium intake, the more significant weight loss was found (Davies, 2000).
Calcium does not increase weight loss
Studies’ results about calcium and weight loss have no middle ground. Of the nine studies included for this position, all results directly state if calcium increased weight loss, or did not. No mixed results occurred within the individual studies. The studies that discussed calcium as playing no major role as a mechanism for weight loss had a better study design. These study designs were stronger because they considered other variables that may affect weight loss, included a more varied study population, and had significantly more subjects. They were carried out for longer periods of time (See TABLE 1 which organizes study specifics) and were not supported by the National Dairy Council as the studies carried out by Michael B. Zemel were which may lead to encouraged results. These better study designs support the hypothesis that calcium does not increase weight loss.
TABLE 1: Comparing details of the five studies of human intake of calcium and weight loss which clarify study design.
Study / Population / Study participants / Length of Study / Results: Calcium does increase weight lossShapses et al / Pre-menopausal/ postmenopausal women / 100 / 25-wk / No
Gunther et al / Women 18-30 yrs old / 135 / 1 year / No
*!Thompson et al / Obese / 72 / 48-wk / No
*Zemel et al / Obese / 32 / 24-wk / Yes
*Zemel et al / Obese African-American / 29 / 26-wk / Yes
*Supported and funded by National Dairy Council
! Michael B. Zemel was involved in this study for support from National Dairy Council
TABLE 1 presents five human studies’ conceptually. The studies results concluding that calcium does not increase weight loss had more study participants and were carried out for longer periods of time compared to studies with contradicting results.
Studies that found that increased calcium intake without caloric restriction did not increase weight loss (See FIGURE 1):
included the general adult population, took more measurements to assess calcium’s role in weight, and considered other variables that affect the body. Calories consumed, protein intake, physical activity may all affect weight loss. Although not every study rejecting calcium’s role in weight loss were thorough about the assessment of these factors, none of the studies finding calcium to aid in weight loss considered these measurements. Because the Gunther et al. (2005) study included women, measurements were taken consistently during days 3-11 of the menstrual cycle and between 7 am and 11 am after a twelve hour fast. Resting heart rate and post exercise heart rate was measured. Estimated VO2max was calculated. The VO2max calculates oxygen intakes during a high intensity exercise test. The measurements taken assume that with higher intake of oxygen, the more efficient the body is, and therefore the more fit. Individuals VO2max can affect weight loss. For the assessment of dietary intake, three-day food records, three-day physical activity records, and lifestyle questionnaires with medical history were collected. Using the above detailed information, nutritionists were able to assess daily energy expenditure to differentiate between weight loss due to lifestyle factors or calcium. These measurements and factors are important to include to more accurately study calcium and weight.
An example of a strong study design which found that calcium does not increase weight loss was conducted by Thompson et al. This study required subjects to have a stable weight over the previous 6 months. Subjects were eliminated if they had a history of an eating disorder, took calcium supplements, and took medication for diabetes or weight loss and numerous other reasons that may affect body weight. Subjects completed two-week weight maintenance by keeping daily food records and exercise logs. Study participants were instructed to exercise at least 30 minutes four times each week throughout the study. A daily food diary was kept as well as the minutes of exercise per day. The primary outcome of this study was weight change at 48 weeks. Secondary outcomes that were additionally assessed to further support conclusion of results included change in body fat, trunk fat, waist circumference, fasting glucose and insulin. Because this study was more detailed with its methods, the results make conclusions more credible and further supports my position.
The counterargument of Zemel et al. study (2004), which found with increased calcium, an increase in body weight (see FIGURE 2) assessed only obese African-American adults. Parts of the study were significantly flawed, which affect the credibility of the study’s conclusion. The specific population of this study prevents the results to be related to general adults. This study lacked the requirement of a medical history. To assess the study participant’s progress, minimal measurements were taken. Besides a 500 caloric deficit, food logs, and weight and fat loss measurements, other lifestyle factors were not considered. Although this study found that with substitution of calcium-rich foods in restricted diet adiposity was reduced, many other factors may have played a significant role in these findings.
A review supporting calcium intake to lose weight, which was one of a few, included for support in the 3-A-Day campaign, may be less credible. Only two human studies are included in this review by Zemel et al. (2004) to conclude calcium increases weight loss. The 3-A-Day campaign’s credibility relies on these studies’ findings. However, when the 3-A-Day campaign attempts to show significant evidence for the conclusion of dairy products for weight loss, most of the information is provided by numerous studies done by Zemel et al. Because his study populations were specific, he was able to reuse his flawed study design to produce more studies for the support of the National Dairy Council’ campaign. He used more specific subjects, such as obese African-Americans, and smaller numbers of subjects, of approximately 30 in his studies. The National Dairy Council webpage providing information about the 3-A-Day campaign lists more studies supporting their claim. This list is misleading because many of the studies that support the claim also involve Michael B. Zemel who has received over $1.7 million dollars for research from the National Dairy Council. It appears as though numerous, unbiased studies have concluded calcium increases weight loss, when in fact, results may be interpreted to satisfy the consumer. These study designs are flawed because important factors that influence weight loss are ignored. Although Michael B. Zemel may be able to produce more studies, the numbers of study results do not significantly support the National Dairy Council campaign. Studies that contradict these findings include most of the same subjects but combine the methodology into a bigger, more inclusive report. So even though numerous studies have shown that calcium increases weight loss, these studies may be too similar in design to be accredited as more support. The studies that found no weight loss with increased calcium alone included adults, which may include obese African-Americans, and had at least two and a half times the number of subjects than the studies that are supported by the National Dairy Council.
The studies of rats and mice had comparable results to the human studies. The similarity among the three studies of rats and mice were the way that calcium was administered in the water source. The study done by Zhang & Tordoff (2004) found no significant effect of dietary calcium on body weight. This study added 30 mM of CaCl2 to a sweetened drinking source. The strength of this study is that a normal diet was maintained to observe weight loss. A weakness was the inability to get the mice and rats to ingest a significant amount of calcium. Because the calcium had a taste and these animals consume small amounts of food and water, the researchers were unable to induce the mice and rats to ingest significant amounts of calcium for needed measurable results. Also, the animals were not fully grown, which may have affected weight change. The study with rats by Papakonstantinou et al. (2003) found a decrease of weight with a high-calcium diet. The calcium was ingested by liquid as well, using nonfat milk. Because the nonfat milk included sucrose (sugar) the weight loss cannot be attributed to calcium alone. Because a total of 840 calories varied between the groups of rats ingesting different amounts of calcium, the amount of weight loss of each group of rats may not be based solely on calcium intake. Studies using mice and rats may be related to human adiposity; however, mechanisms of the body are often times quite different.
Conclusion
A few studies and reviews show evidence that calcium can significantly improve weight loss in adults, rats and mice. Other studies conclude the opposite. The studies that found that calcium does not increase weight loss had stronger study designs. These studies included more subjects, were carried out for a longer period of time, and considered more variables. Oftentimes, the methodologies of these studies were more rigid with nutritionist interventions and counseling, because the diet regulation was such a crucial component of the studies. Although the National Dairy Council’s 3-A-Day campaign has support through the studies of Michael B. Zemel and a few others, these studies are excluding crucial factors that may affect calcium’s role in weight loss.
Reference:
Davies, Michael K., Robert P. Heaney, Robert R. Recker, Joan M. Lappe, M. Janet Barger-Lux, Karen Rafferty, Sharilyn Hinders (2000). Calcium Intake and Body Weight. The Journal of Clinical Endocrinology and Metabolism 85(12) 4635-4638.