Observational studies have shown an inverse association between dietary calcium intake and body weight, and a causal relation is likely. However, the underlying mechanisms are not understood.
We examined whether high and low calcium intakes from mainly low-fat dairy products, in diets high or normal in protein content, have effects on 24-h energy expenditure (EE) and substrate oxidation, fecal energy and fat excretion, and concentrations of substrates and hormones involved in energy metabolism and appetite.
In all, 10 subjects participated in a randomized crossover study of three isocaloric 1-week diets with: low calcium and normal protein (LC/NP: 500 mg calcium, 15% of energy (E%) from protein), high calcium and normal protein (HC/NP: 1800 mg calcium, 15E% protein), and high calcium and high protein (HC/HP: 1800 mg calcium, 23E% protein).
The calcium intake had no effect on 24-h EE or fat oxidation, but fecal fat excretion increased ∼2.5-fold during the HC/NP diet compared with the LC/NP and the HC/HP diets (14.2 vs 6.0 and 5.9 g/day; P<0.05). The HC/NP diet also increased fecal energy excretion as compared with the LC/NP and the HC/HP diets (1045 vs 684 and 668 kJ/day; P<0.05). There were no effects on blood cholesterol, free fatty acids, triacylglycerol, insulin, leptin, or thyroid hormones.
A short-term increase in dietary calcium intake, together with a normal protein intake, increased fecal fat and energy excretion by ∼350 kJ/day. This observation may contribute to explain why a high-calcium diet produces weight loss, and it suggests that an interaction with dietary protein level may be important.
There has recently been accumulating evidence to support the hypothesis that the dietary intake of calcium may play an important role in body weight regulation. Several reports have found inverse associations between calcium intake and body weight.1,2,3,4,5,6 In their analysis of data from NHANES III, Zemel et al2 observed an inverse association between relative risk of obesity and calcium intake. Similar observations have been reported by others.5 Davies et al1 reanalyzed data from five studies (one intervention and four observational studies) that were originally designed to examine the effect of dietary calcium on bone health. In two of these studies (cross-sectional studies on young women), they observed that an increase in dietary calcium to protein ratio of 1.0 mg/g was associated with a 0.186 kg/m2 decrement in body mass index (BMI). Including all four observational studies, they concluded that differences in calcium intake could explain around 3% of the variation in body weight. However, all the above reports were based on observational studies, and because of the possibility of unaccounted confounding factors, they cannot establish whether the relation is causal, that is, a change in calcium intake producing a change in body weight.
Very few intervention studies have been conducted examining the effect of calcium intake on body weight. Zemel et al.4 examined the effect of calcium supplementation on weight and fat loss in obese adults on calorie-restricted diets They found that a high-calcium diet (1200–1300 mg/day) resulted in greater weight and fat loss in humans compared to a low-calcium diet (400–500 mg/day). In addition, they found that calcium from dairy products had a more profound effect than calcium from supplements. The mechanism of this additional dairy effect is not yet clear. In their analysis of data from a randomized controlled intervention study, which was designed to examine the effect of calcium supplementation (1200 mg/day) on bone mineral density, Davies et al1 found that both groups lost weight during the intervention period, but the intervention group lost 0.346 kg/y more than the control group. It therefore seems likely that at least part of the effect seen in the observational studies was due to the differences in calcium intake.
A number of different mechanisms have been suggested to be responsible for the effect of a high-calcium intake on energy balance (EB). One possible explanation is reduced absorption of fat in the gut, another that intracellular calcium has a regulatory role in fat metabolism by influencing lipolysis, fat oxidation, and lipogenesis.2,7,8 These effects could influence appetite regulation and energy expenditure (EE).
In the present study, we examined whether high- and low-calcium intakes, mainly from low-fat dairy products, in diets with high or normal protein contents, have an effect on 24-h EE and substrate oxidation, fecal fat excretion, and plasma concentrations of substrates and hormones involved in energy metabolism and appetite.
Subjects and methods
In all, 10 subjects (eight women and two men) were recruited through advertising at the University. Subjects had to be healthy, between 18 and 50 y old, and moderately overweight. The exclusion criteria were lactose intolerance, infections or metabolic diseases, pregnancy or lactation, and use of dietary supplements. After having received verbal and written information about the study, all subjects gave written consent. The study was carried out at the Department of Human Nutrition, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark, and was approved by the Municipal Ethical Committee of Copenhagen and Frederiksberg in accordance with the Helsinki-II declaration (KF 01-144/02). Subjects received 5000Dkr. (∼800dollar;) on completion of all tests. Characteristics of the subjects are presented in Table 1.
The study had a randomized, crossover design, where 1 week of controlled intake of three different isocaloric diets was examined. The subjects were randomized to the sequence of the three diets. A baseline measurement was executed before the first diet-period. Between each diet-period there was a 1 week wash-out period where the subjects consumed their habitual diets. The design is illustrated in Table 2.
The three different diets contained low calcium and normal protein (LC/NP), high calcium and normal protein (HC/NP), or high calcium and high protein (HC/HP) (Table 3). The computer database of foods from the National Food Agency of Denmark (Dankost 2000, National Food Agency of Denmark, Søborg, Denmark) was used to calculate the content of micro- and macronutrients. Energy and calcium contents were measured as described below. The main source of calcium and protein was low-fat dairy products. Each diet was composed of one breakfast dish, one lunch dish and one snack, and two different dinner meals, which were served on alternate days. We aimed to make the content of dietary fiber and vitamin D identical in all three diets (Table 3). The subjects received a standard diet containing 16% of energy (E%) from protein, 56 E% carbohydrate, 28 E% fat and 76 mg calcium/MJ during the baseline measurement in the respiratory chamber.
The diets were prepared at the Department from normal Danish food items according to each subjects' individual energy requirement and adjusted to the nearest 1 MJ. The subjects' energy requirements were determined by the following formula.9:
However, several studies at the Department have shown that 24-h EE calculated using this formula is 10 to 15% lower than 24-h EE measured in the respiratory chamber (unpublished data). To compensate for this difference, an additional 10% of the calculated 24-h EE was added. Spontaneous physical activity (SPA) was estimated to 5.6% for females and 5.8% for males and duration of exercise (DE) to 30 min.9 Body composition was measured at baseline by bioelectrical impedance method using an Animeter (Unitech, Humble, Denmark). Fat-free mass (FFM) and fat mass (FM) were calculated as described elsewhere.10
On weekdays, breakfast and lunch were consumed at the Department, whereas snacks and dinner were given to the subjects to eat at home. All meals for the weekend were supplied to the subjects. The subjects were instructed to adhere strictly to the supplied diet. However, the subjects were allowed to add spices and consume water, tea, coffee, and diet soft drinks ad libitum. Only caffeine-free coffee and tea were allowed during the stays in the respiratory chamber.
The subjects' habitual diet was assessed by a 7-day, weighed food record. The subjects were given both verbal and written instructions on how to perform a 7-day, weighed food record, and digital weights were supplied. The computer database Dankost 2000 was used in the calculations of energy and nutrient composition of the diets.
Anthropometrics and body composition
Height was ascertained at baseline to the nearest centimeter using a Seca stadiometer (Hultafors, Sweden). Weight and waist circumference were measured at baseline, on the morning of the first day of every diet-period, and on the morning after the last day of every diet-period (Table 2). The subjects were fasting on all occasions. Weight was measured in kilograms with one decimal by a Lindetronic 8000 scale (Copenhagen, Denmark) and waist circumference was measured to the nearest ½ centimeter by tape.
Dual energy X-ray absorptiometry (DEXA) measurements (Lunar DPX-IQ, Lunar Radiation Corp., GE, Madison, WI, USA) were performed as whole body scans in the slow mode,11 with separate assessment of the three compartments: FM, total soft body mass, and total bone mineral content (BMC). FFM was calculated as total soft body mass minus FM plus BMC. For quality assurance and equilibration, a calibration block was scanned each morning. A spine phantom was scanned on a weekly basis; the coefficient of variation (CV%) was 1%. The same skilled laboratory technician performed all DEXA scans.
Blood pressure and pulse were measured at baseline and on the morning of the first day of every diet-period and the morning after the last day of every diet-period. They were measured, in the supine position after 10 min of rest, with an automatically inflating cuff (UA-743, A&D Company Ltd, Tokyo).
EE and substrate oxidation
The 24-h EE was measured in two open-circuit respiratory chambers as described elsewhere.12 The measurement started at 0900 and continued for 24 h. Basal metabolic rate (BMR) was measured during the last hour of the stay. During the 24-h stay, subjects followed a standard protocol including two periods of 15 min of cycling on an exercise bicycle (75 W) (Monark 814E, Monark AB, Varberg, Sweden) and two periods of walking back and forth 25 times in the chamber. Room temperature was kept at 24°C during daytime hours (0900 to 2300) and at 18°C during the night and during assessment of BMR. SPA indicates the percentage of time in which the subject was active to a detectable degree. It was assessed by two microwave radar detectors (Sisor Mini-Radar; Statistic Input System SA, Lausanne, Switzerland), which continuously emitted and received signals. When the radar detects a moving object a signal is generated and received by the transceiver. Heart rate was measured using a portable ECG telemetry recorder (Dialogue 2000 type 2070-14 XTNJ, Danica Electronics, Rødovre, Denmark). Body temperature was assessed by a digital thermometer (Becton Dickinson, Franklin Lakes, NJ, USA).
The 24-h EE and oxidation of carbohydrate, fat, and protein were calculated from the gas exchange and urinary nitrogen measurements using the constants of Elia and Livesey.13 Protein oxidation was assumed to be constant during the day.
where RQnp is nonprotein respiratory quotient.
The 24-h urine samples were collected during the stays in the respiratory chamber. Urine volume and density was measured and a sample of 2 ml was frozen at −20°C until further analysis. Nitrogen content was measured in a specimen using the Dumas method with a nitrogen analyser (NA1500, Carlo Erba Strumentazione, Milano, Italy).
Urinary calcium was measured in the 24-h urine sample from the last day of every diet-period. The concentration was measured using atomic absorption on a Spectra AA-200 (Varian, Victoria, Australia). The CVintra% was 2.1 and CVinter% was 2.9.
Venous blood samples were drawn at baseline on the morning of the first day of every diet-period and on the morning after the last day of every diet-period. The subjects had fasted overnight. Blood for determination of serum free fatty acid (FFA), insulin, leptin, triacylglycerol (TG), total cholesterol, HDL, LDL, triiodothyronine (T3), and thyroxine (T4) was centrifuged at 2800 × g for 15 min at 4°C. Serum was extracted and the samples were stored at −20°C until later analysis. FFA was determined by an enzymatic colorimetric method (Wako NEFA test kit, NEFA C, ACS-ACOD method, Wako Chemicals Inc., Richmond, VA, USA) using a Cobras Mira plus (Roche, Basel, Switzerland). CVintra% and CVinter% were 7.2 and 3.4%, respectively. TG was measured by an enzymatic, end point method (Test-Combination Triacylglycerol (GPO-PAP) kit, Roch, Basel, Switzerland) using a Cobras Mira plus (Roche, Basel, Switzerland). The CVintra% and CVinter% were 0.5 and 3.6%, respectively. HDL was measured by the homogeneous enzymatic colorimetric test (HDL-C plus 2nd generation kit lot. no. 642538, Roche Diagnostics, Basel, Switzerland) using a Cobras Mira plus (Roche, Basel, Switzerland). CVintra% and CVinter% were 1.0 and 5.1%, respectively. LDL was measured by homogeneous enzymatic colorimetric test (LDL-C plus 2nd generation kit lot. no. 64632901, Roche Diagnostics, Basel, Switzerland) using a Cobras Mira plus (Roche, Basel, Switzerland). Total cholesterol was measured by an enzymatic end point method (CHOD-PAP) (cholesterol kit, Roche, Basel, Switzerland) using a Cobras Mira plus (Roche, Basel, Switzerland). CVintra% was 0.9 and CVinter% was 1.2. T3 was measured by fluoroimmunometric using an AutoDELFIA™ (AutoDELFIA triiodothyronine kit B029-101/B029-104, Wallac O, Turku, Finland). CVintra% was 3.0–3.5 and CVinter% was 1.3–1.5 according to Wallac Oy (Turku, Finland). T4 was measured by fluoroimmunometric using an AutoDELFIA™ (AutoDELFIA thyroxine B030-101/B030-104, Wallac O, Turku, Finland). CVintra% was 2.8–3.5 and CVinter% was 1.5–2.1 according to Wallac Oy (Turku, Finland). Insulin was determined by solid-phase, two-site fluoroimmunometric (Insulin kit B080-101, Wallac Oy, Turku, Finland) using an AutoDELFIA™ (Wallac Oy, Turku, Finland). The CVintra% and CVinter% was 2.4 and 2.9%, respectively. Leptin was determined by radioimmunoassay (Human Leptin RIA kit, DRG Diagnostic, Marburg, Germany) using a gamma counter (Wallac LKB 1272 Clinigamma Wallac Oy, Turku, Finland). The CVintra% and CVinter% were 6.2 and 8.2%, respectively.
All feces excreted were collected in preweighed containers during the last 3 days of each diet-period. In addition, the subjects completed a questionnaire on daily defecation frequency during every diet-period. The fecal samples were weighed and frozen at −20°C. Before analysis, the samples were freeze-dried and homogenized, and samples from the same diet-period were pooled. Fecal energy was obtained using a bomb calorimeter (Ika-calorimeter system C4000 Heitersheim, Germany). Before fat content was measured, the samples were acid hydrolyzed with 3 N HCl. Total fat content was measured by a method modified after Bligh and Dyer.14
Calcium was measured by atomic absorption spectrophotometry using a PYE UNICAM SP9 atomic absorption spectrophotometer (Philips Electron Optics, Mahwah, NJ, USA). Prior to analysis, the samples were destroyed by dry-ashing at 525°C for 6 h and the ashes were dissolved in acid (6.5% HNO3). The solution was diluted with a lanthanum chloride solution before the concentration was measured.
Transit time was measured in six subjects. On the second, third, and fourth day of each diet-period, the subjects consumed a capsule containing nonabsorbable, radio-opaque markers (Medifact, Göteborg, Sweden). Markers consumed on the same day had the same shape, where as markers consumed on different days differed in shape. The subjects consumed 20 markers/day during the first two diet-periods and 60 markers/day during the last. Transit time was measured as described elsewhere.15
Samples of each diet were freeze-dried and homogenized. Energy content was obtained using a bomb calorimeter (Ika-calorimeter system C4000 Heitersheim, Germany). Before calcium content was measured, the samples were lyophilized and microwave digested (MES-1000, CEM Corporation, Matthews, NC, USA) with HNO3 65%, suprapur (Merck, Darmstadt, Germany) and H2O2 30%, suprapur (Merck, Darmstadt, Germany). Calcium was measured by atomic absorption spectroscopy SpectraAA-200 VARIAN (Varian Techtron Pty. Limited, Victoria, Australia) after dilution with lanthaniumoxide solution (Merck, Darmstadt, Germany). Standards were prepared from a 1000 mg/l Ca standard (Tritisol®, Merck, Darmstadt, Germany) by dilution with lanthaniumoxide solution. A reference diet (Standard Reference Material 1548a, Typical Diet, National Institute of Standards and Technology, Gaithersburg, MD, USA) was analyzed in the same run.
All values are expressed as mean±s.d. Differences between the three diets in substrate oxidation, EE, RQ, body composition, blood parameters, and anthropometric measurements were analyzed by mixed model for analysis of covariance. Values from after the diet-period were included as the dependent variable and subjects as a random variable. Adjustments were also made for various covariables. Baseline values were not included in the analyses. Differences in the fecal and the urinary parameters were analyzed by analyses of variance (ANOVA), with subjects included as a random effect. Tukey correction for multiple tests was applied for multiple post hoc comparisons. Differences between the values measured before and after the diet-period were analyzed by a paired t-test. Correlation between calcium intake and fat excretion was calculated using Pearson's correlation coefficient. A linear regression model was used to relate calcium intake to fat excretion. All statistical analyses were performed using Statistic Analysis Package, SAS© (SAS Institute, Cary, NC, USA). The level of significance was set at P<0.05.
All 10 subjects completed all three diet-periods. The subjects' habitual intake of macronutrients and calcium is presented in Table 4. The 24-h EE estimated from body composition and physical activity levels did not differ from 24-h EE measured in the respiratory chambers at baseline (10.0±1 vs 9.3±1 MJ).
Changes in anthropometric characteristics are presented in Table 5. There was a slight decrease in body weight during all three diet-periods (P<0.05), but no difference between the three diets. There was no effect of diet on FFM or FM.
EE and substrate oxidation
EE, substrate oxidation, and 24-h EB (calculated as 24-h energy intake (EI)−24-h EE) are presented in Table 6. No significant overall effect of diet on 24-h EE or BMR was found, whether unadjusted or adjusted for SPA, EI, FFM, and FM. Also, no significant effect of diet was found on 24-h EB. In addition, both 24-h EE, BMR, and 24-h EB were unchanged in the three diet-periods. There was a small significant fall in RQnp from the first to the last day in all three diet-periods. However, diet had no significant overall effect on RQnp measured on the last day of the diet-period when adjusted for EB. Including the fecal energy loss in 24-h EB did not alter the result.
There was a significant effect of diet on carbohydrate oxidation when adjusted for EB (P=0.01). Carbohydrate oxidation was higher during the LC/NP (P=0.05) and the HC/NP (P=0.01) diet than during the HC/HP diet. Similarly, there was an overall effect of diet on protein oxidation when adjusted for EB (P<0.001). Protein oxidation during the HC/HP diet was significantly higher than during the HC/NP (P<0.001) and the LC/NP (P<0.001) diet.
Excretion of energy, fat, and calcium
The fecal moisture content was <80% during all three diets in all subjects. At baseline only six subjects were included, as the last four subjects did not defecate during the 24-h stay in the respiratory chamber. During the rest of the study fecal collections from two subjects were excluded due to technical problems.
Fecal weight is presented in Table 7. The fecal dry weight was 39% higher in the HC/NP diet than in the LC/NP diet (NS) and 29% higher than in the HC/HP diet (NS). There was no difference between the LC/NP and the HC/HP diets. Similar differences were observed in fecal wet weight. Transit time was 61±30, 54±22, and 57±15 h during the LC/NP, HC/NP, and HC/HP, respectively. Diet had no significant effect on transit time.
Total fecal fat and energy excretion during baseline and the three diet-periods are presented in Table 7. There was a significant effect of diet on total fat excretion (P=0.0002). The fecal total fat excretion increased ∼2.5-fold during the HC/NP diet as compared to the HC/HP and LC/NP diets (P<0.05). There was no significant difference between the total fat excretion during the HC/HP and the LC/NP diets. The proportion of ingested fat that was excreted daily during the HC/NP diet was 18.0±8%, whereas in the LC/NP and HC/HP diets it was only 7.3±3 and 7.5±3%, respectively.
There was a significant effect of diet on energy excretion (P=0.026). The fecal energy excretion increased by 55% during the HC/NP diet as compared with the HC/HP and LC/NP diets (P<0.05), with no difference between the two latter diets. The difference in fecal fat excretion could explain about 80% of the difference in fecal energy. There was a significant positive correlation between calcium intake and fecal fat excretion (r=0.56, P=0.007), when data from baseline and from all three diet-periods were included. In order to further understand the relationship between calcium intake and fat excretion, a linear regression model including calcium intake was employed. The slope was 0.0054 (P=0.0066) and adjusted r2 was 0.2803.
Diet had a significant effect on fecal (P=0.0016; ANOVA) and urinary (P<0.0001; ANOVA) calcium excretion. Fecal calcium excretion was lower in the LC/NP diet (675±331 mg/day) than in the HC/HP (1821±777 mg/day; P=0.001) and the HC/NP (1865±739 mg/day; P=0.002) diets. Urinary calcium excretion was higher during the HC/HP diet (188±53 mg/day) than during the LC/NP (102±47 mg/day; P<0.0001) and the HC/NP (113±46 mg/day; P<0.0001) diets.
There was no overall effect of diet on total cholesterol, HDL, LDL, FFA, or TG measured after the diet-period when adjusted for 24-h EB, sequence of the diets and concentration measured before the diet-period (Table 8). Serum concentrations of insulin, leptin, T3, and T4 did not change from before to after in any of the three diet-periods (Table 8). There was no overall effect of diet on insulin, leptin, T3, and T4 measured after the diet-period when adjusted for 24-h EB, sequence of the diets and concentrations measured before the diet-period.
Blood pressure and heart rate
Diet had no significant effect on either systolic or diastolic blood pressure, or heart rate measured after the diet-period when adjusted for sequence of the three diets and baseline blood pressure values (Table 5).
The present study evaluated the short-term effects of high vs low dietary calcium intakes in isocaloric diets taking dietary protein level into consideration. The major findings are that a high-calcium diet has no effect on EE, fat oxidation, SPA, or thyroid hormone concentrations, but that it increases fecal fat and energy excretion substantially in a diet with a normal protein content.
The fecal fat excretion was increased by HC/NP diet from about 7 to about 18% of the consumed fat. Quantitatively this fecal energy loss is highly relevant for body weight regulation. There was a difference between the LC/NP and the HC/NP diet of 8.2 g/day in total fat excreted. This corresponds to an increase of 312 kJ/day or 113.9 MJ/y. Assuming that an increased fat excretion of 14.64 MJ/y (3500 kcal) produces a weight loss of 0.45 kg/y (1 pound), and that the subjects maintain the same EI, this would correspond to a weight loss of 3.5 kg/y. In the present study, there was no difference between the two diet-periods in weight loss or body composition, which is in accordance with the fact that the predicted weight loss would be only 67 g/week, which is below detection limit for the scale.
The mechanism by which calcium increases fat excretion is probably an interaction between calcium and fatty acids, resulting in the formation of insoluble calcium fatty acid soaps, and hence in reduced fat absorption. There was a difference between the LC/NP and the HC/NP diet of 1190 mg/day in fecal calcium excreted, which corresponds to about 60 Meq of calcium. The maximum amount of fat that can be bound to this amount of calcium is about 60 mmol fatty acids. Assuming that fatty acids have a molecular mass of about 270 g/mol, this corresponds to a maximum increase in fat excretion of 16 g/day. Of course, not all calcium would be available for binding fatty acids. Thus, it seems likely that the increase in excreted fat of 8.2 g/day found in the present study can be explained by the formation of calcium fatty acid soaps.
The results from the present study are in agreement with other studies showing an increase in the fecal fat excretion when calcium intake is increased.6,7,8,16 Shahkhalili et al8 showed, in a crossover study, that supplementation of chocolate with 0.9W% calcium, as part of a diet providing 14E% protein and 39E% fat, resulted in a two-fold increase in total fecal fat excretion (4.4–8.4 g/day). This is somewhat similar to our results. Denke et al7 compared a control diet (11E% protein and 34E% fat) with a low content of calcium (410 mg/day) with a fortified version providing a total of 2200 mg calcium, and found that fecal excretion of saturated fat, as related to intake, increased from 6 to 13%. Welberg et al16 examined the effect of supplementation with calcium (0, 2, or 4 g/day) in 24 subjects consuming their habitual diet. Total fat excretion was 6.8, 7.4, and 10.2% of fat intake, which is slightly less than the effect observed in the present study.16 In our study, the fecal fat excretion was higher compared with these other studies.7,8,16 The fecal fat excretion of 10.5 g/day at baseline may seem high, but is not when the high habitual dietary calcium intake of the subjects are taken into account. We found a positive correlation between calcium intake and fecal fat excretion. An increase of 1000 mg in calcium intake resulted in an increase of 5.4 g in fat excretion. Moreover, we have validated the findings by showing corresponding changes of the fecal energy excretion measured by an independent technique (bomb calorimetry). Besides this, the previous studies7,8,16 have all used either fortified food or dietary supplements; in our study, we used dairy products, which might contain other bioactive components able to interact with the fatty acids, thereby increasing the fecal fat excretion. Furthermore, the different study designs may have led to different results.
Papakonstantinou et al investigated in rats the effect of a high-calcium diet based on dairy products on EE and fat absorption in rats. In agreement with the results from our study, they were able to show quite a substantial increase in fecal fat and energy excretion and no significant difference in EE.6 To our knowledge, no other studies in humans have tested the effect of calcium from dairy products on fecal fat excretion.
The calcium content of the low-calcium diet was about 500 mg/day. According to the latest nation-wide survey of dietary habits in Denmark only about 10% of adults have a daily calcium intake below this level, and only 10% have a daily calcium intake of 1850 mg/day or more.17 The adult American population has an average daily intake of 761 mg calcium; only 21% of this population has an intake of the recommended 1000 mg.18 All three diets in the present study were prepared from normal Danish food items and it is therefore realistic to propose that such diets can be consumed on a regular basis.
There was no difference in fecal fat excretion between the LC/NP and the HC/HP diet, indicating that high-calcium intake only has an effect on fat excretion when the protein intake is normal (15E%). Protein is suggested to be more satiating and thermogenic than carbohydrate, and a high-protein diet produces more weight loss than a high-carbohydrate diet.19 Our major aim, therefore, in varying the protein level was to take into consideration that some of the observations, linking high-calcium intake to lower body weight, may have been confounded by a high-calcium diet also being a high-protein diet because of the concomitant of calcium and protein content, in milk, cheese, and other dairy products. It was thus surprising that the high-calcium diet only increased fecal fat loss in the context of a normal dietary protein level. A possible explanation for this is that calcium is, in part, reversibly bound to dietary protein in the upper gastrointestinal tract where fat digestion and absorption occurs. Casein is a highly phosphorylated protein and calcium may bind to the phosphoserine residues of casein. The calcium–protein complexes, formed in the presence of a high dietary protein level, may use up the calcium, which would otherwise be used in the formation of calcium fatty acid soaps. In agreement with our results, Yuangklang et al20 found that soy protein, which is a poorly phosphorylated protein, but not casein, decreased fat digestibility in veal calves. They also found a significantly higher excretion of bile acids among calves fed high calcium and soy protein than calves fed high calcium and casein. They argued that this may be caused by higher amount of calcium phosphate sediment in the small intestine after the comsumption of soy protein and that bile acids bind to this sediment, thus impairing the participation of bile acids in the process of fat digestion. In the present study, the excretion of bile acids was not measured and it is therefore not known whether the excretion was affected by the different diets. Moreover, more calcium is probably absorbed in the presence of protein, making less calcium available for binding to fat.21 A more effective calcium absorption on the HC/HP than on the HC/NP diet was also suggested by a 66% higher urinary calcium excretion on the HC/HP diet. It was attempted to make the dietary fiber content in all three diets identical, and it is therefore unlikely that the difference in fecal fat excretion can be explained by differences in fiber content. In a study examining the effect of energy restricted high-protein diets either high (2400 mg/day) or low (500 mg/day) in calcium content, they found no diet effect on weight loss.22 This confirms the results of our study.
In our study, the subjects were in slightly positive 24-h EB on all three diets, probably due to a lower physical activity during the stay in the respiration chamber compared with their habitual physical activity. However, since the 24-h energy balance and the slight weight loss were very similar following the three diets, energy balance is unlikely to confound the results.
Protein oxidation was higher during the HC/HP diet than during the other two diets. This was compensated for by a decrease in carbohydrate oxidation during this period. Fat oxidation increased during all three diets, but we failed to find any effect of the high vs low calcium intakes on RQ or fat oxidation rates. This is apparently in disagreement with a recent cross-sectional study by Melanson et al. They showed a positive correlation between calcium intake and fat oxidation (r=0.38, P=0.03), and an inverse correlation between calcium intake and 24-h RQ (r=−0.36, P=0.04).23 However, the associations were not very strong and were of borderline statistical significance, and it is likely that the calcium increased fat oxidation by producing a more negative EB due to reduced absorption of dietary fat.
During the two high-calcium diets in the present study, a trend to a minor but still important decrease in blood pressure was observed. On the HC/NP diet, there was a 2 and 8% decrease in the systolic and the diastolic blood pressure, respectively. On the HC/HP diet there was a 3 and 5% decrease in the systolic and the diastolic blood pressure, respectively. Consuming fat-reduced dairy products has previously been shown to reduce blood pressure.24
In summary, we found no effects of a high-calcium intake on EE, fat oxidation, SPA, or thyroid hormone concentrations, whereas, as part of a diet with normal protein content, it produced a clinically significant increase in fecal fat and energy excretion. The study did not test the effect on appetite and EI, so it is possible that calcium may also exert metabolic effects that can translate into a suppression of EI. Moreover, effects on energy metabolism cannot be excluded as we tested only the short-term effects and 1 week may be insufficient to reach a new steady state with the requisite intracellular calcium concentration and subsequent gene expression.
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We thank John Lind, Inge Timmermann, Helle R Christensen, Kirsten B Rasmussen, Martin Kreutzer, Charlotte Kostecki, Yvonne Rasmussen, and Karina G Rossen for their assistance. This work was financially supported by the Danish Dairy Board, Aarhus, Denmark and The Directorate for Food, Fisheries and Argi Business, the Danish Ministry of Food, Agriculture and Fisheries, Copenhagen, Denmark.
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Jacobsen, R., Lorenzen, J., Toubro, S. et al. Effect of short-term high dietary calcium intake on 24-h energy expenditure, fat oxidation, and fecal fat excretion. Int J Obes 29, 292–301 (2005). https://doi.org/10.1038/sj.ijo.0802785
- dietary calcium
- energy expenditure
- fecal fat excretion
- fat oxidation
- body weight
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