Although recommended levels of dairy have been shown to augment weight loss during energy restriction when compared to low dairy intakes, little is known about the effects of recommended levels of dairy during weight maintenance. We investigated the effects of recommended levels of dairy compared to low levels of dairy across 6 months of weight maintenance but found no differences between groups for body weight or components of body composition.
The premise of this investigation was that correction of dietary calcium and dairy insufficiency may attenuate weight regain following successful weight loss. Accordingly, it was important to have a clear comparison of inadequate versus adequate levels of intake, as supplementation of an adequate or nearly adequate diet would be predicted to exert little or no effect. For example, previous studies of the effects of dairy on adiposity during energy restriction demonstrated significant effects when the un-supplemented group had calcium and dairy food intakes of <600 mg and <1 serving/d, respectively [5–7], while increasing the dairy intake of a group consuming a more moderate level of calcium (~800 mg/d) during comparable energy restriction exerted no effect . Consequently, this study was designed to distinguish between clearly inadequate levels of calcium (<600 mg/day) and dairy (<1 serving/day) with clearly adequate levels (>1,000 mg calcium and >3 dairy servings/d), and our dietary intake data demonstrate that these parameters were met.
The adherence to treatment during weight maintenance was excellent, with the recommended dairy group showing ~3 fold greater dairy intake compared to the low dairy group. This was reflected in a significant decrease in 1,25-(OH)2-D levels in the recommended dairy group, while no change was seen in the low dairy group. Attrition was 17.4% in the recommended dairy group compared to 14.3% in the low dairy group indicating that higher levels of dairy were well tolerated. Metabolic profile was not different between the recommended compared to the low dairy group indicating that increased consumption of dairy products did not have a negative impact on the metabolic profile.
Of interest, the low dairy group had decreased energy intake compared to the recommend dairy group at all time points yet maintenance of body weight and fat were not different. This suggests that diets with recommended levels of dairy may be higher in energy content while producing similar effects on body weight and fat as diets low in dairy. The reason for this is unclear; however, the recommended level of dairy group had a trend towards greater RMR during weight maintenance compared to the low dairy group (p = 0.08) and a significantly lower RQ (p = 0.01), indicating greater fat oxidation. Greater RMR may impact energy balance by allowing a greater energy intake for the recommended dairy group without increased weight gain when compared to the low dairy group. Additionally, the recommended dairy group also may have benefited from increased fat oxidation compared to the low dairy group, and this also may have influenced energy balance.
In support of this, calcitriol inhibits lipolysis and fat oxidation , and suppressing circulating calcitriol by increasing dairy food intake as observed in the present study has been reported to result in increased lipolysis in both mice [3, 4, 23] and humans [6, 7]. Moreover, Gunther et al  recently demonstrated that chronic consumption (one-year) of a dairy-rich high calcium diet resulted in a significant (~two-fold) increase in post-prandial fat oxidation following a liquid meal challenge compared to subjects maintained on a low-calcium diet. Further, in a randomized controlled crossover study testing the effects of low- and high-dairy diets on substrate oxidation whole-room calorimetry Melanson et al  demonstrated that feeding a high dairy diet under energy deficit conditions resulted in a significant 30 g increase in 24-hour fat oxidation compared to the low dairy diet. This increase in fat oxidation represents an additional 270 kcal/day, a value in the same range as the increase in energy intake on the recommended dairy diet in the present study (248 kcal for the first half of maintenance and 200 kcal for the second half of maintenance), suggesting that an increase in self-reported energy intake in subjects consuming the recommended level of dairy may have been compensated for by a comparable increase in fat oxidation. These values also are consistent with data from Harvey-Berino et al . Although they reported no effect of dairy on weight or fat loss in overweight and obese adults over a one-year period of a prescribed 500 kcal/day deficit, their data demonstrate that the high dairy group maintained an energy deficit of only 314 and 224 kcal/day at 3 and 12 months, respectively, compared to respective deficits of 442 and 402 kcal/day in the low dairy group. Thus, the high dairy group experienced comparable weight loss while consuming an additional ~150 kcal/day. In a similar randomized study, Thompson et al  reported similar weight loss in moderate and high dairy groups prescribed a 500 kcal/day deficit, but those consuming the high dairy diet consumed significantly more energy (~150 kcal/day) while still attaining the same weight and fat loss. Accordingly, we suggest that greater fat oxidation in the present study may have permitted a corresponding increase in energy intake in subjects consuming the recommended level of dairy intake compared to those on low dairy intakes without adversely affecting body weight or body fat.
An additional consideration is the potential direct effect of recommended vs. low levels of dairy intake on appetite and food consumption. Dairy products have been proposed to increase satiety and attenuate food intake due to both protein-induced satiety [41, 42] and to the caseinomacropeptide which is released during digestion of dairy protein and stimulates cholecystokin release . However, Hollis and Mattes  recently reported that feeding three daily dairy servings for seven days in a randomized cross-over study resulted in a significant increase in energy consumption (209 kcal/day) compared to the low dairy period. This number is remarkably consistent with the increased energy consumption by the recommended dairy group in both the present study and earlier reports [8, 16]. Thus, although Hollis and Mattes reported that the additional energy provided by supplementary dairy products is not fully compensated for by a reduction in subsequent energy intake , these data suggest that subjects consuming recommended levels of dairy operate at a lower metabolic efficiency which may result in a shift to greater fat oxidation compared to individuals consuming low levels of dairy. Consequently, the additional energy intake does not result in corresponding gain in weight or fat. Moreover, Ochner and Lowe  recently reported that greater calcium intake (primarily derived from dairy sources) inversely predicted weight gain following weight loss by overweight and obese women only when controlling for energy intake. Higher energy intake significantly predicted weight regain only when controlling for changes in dietary calcium intake. Accordingly, their data indicate that weight gain from excess energy intake following weight loss is attenuated by attaining adequate levels of dairy calcium intake.
There were significant site differences with respect to weight change during the maintenance phase. During the first three months of maintenance, the low dairy group at UT exhibited weight regain that was significantly attenuated in the recommended dairy group; in contrast, the KU cohort exhibited continued weight loss during the first three months of the maintenance phase. Both patterns are common in studies of regain, with some extending adherence to behavioral strategies learned during weight loss into the early ad libitum dietary phase while others demonstrate rapid regain, although longer term studies consistently demonstrate regain within 12 months. Although consistent methodology was used across the two sites, it appears that there were site differences in the retention of the behavioral strategies acquired by subjects during the weight loss phase. Nonetheless, the effects of recommended dairy intakes on fat oxidation as evidenced by RQ changes and on the ability to consume more food energy than low dairy consumers without adversely affecting body weight or body composition was consistent across the two sites in both separate and combined analyses.
This study was conducted in free-living outpatients, with attendant limitations of adherence to protocol and under-reporting of energy intake. Nonetheless, key strengths of this investigation include its sample size (n = 338 enrolled, 270 completed) and adherence to diet, the latter of which is supported by confirmation of anticipated suppression of 1,25-(OH)2-D in the recommended dairy group during the maintenance phase.