It is likely that the addition of glucose slowed gastric emptying, or improved HMB clearance. Recently a new delivery method of HMB, administered as a free acid, has been investigated [30]. The free acid form is called beta-hydroxy-beta-methylbutyric acid and can

be designated as HMB-free acid (HMB-FA). The initial research studies have utilized HMB-FA associated with a gel, containing a buffering mechanism (K2CO3) that raises the pH to 4.5. Commercially, HMB has only been available in the PF-04929113 order calcium salt form (HMB-Ca) as a powder, which has generally been supplemented in capsule form. Moreover, it was previously thought that because calcium dissociated relatively easily from HMB-Ca (10–15 minutes in the gut), there would be no difference selleck products in digestion kinetics between HMB-Ca and HMB-FA [31]. However, this is not the case MK1775 as comparison of 0.8 g of HMB-FA to 1.0 g HMB-Ca (equivalent amounts of HMB) resulted in a doubling of peak plasma levels in one-fourth the time (30 vs. 120 minutes) in the HMB-FA compared with the HMB-Ca [30] (Figure 2). Moreover, area under the curve analysis of HMB concentrations over 180 minutes following ingestion was 91-97% greater in the HMB-FA than

the HMB-Ca form. The half-life of HMB in plasma when given as HMB-FA and HMB-Ca were found to be approximately Bacterial neuraminidase three- and two and a half hours, respectively [30]. Interestingly, even with greater peak plasma concentrations of HMB, urinary losses were not different

between the two HMB forms. Perhaps the most intriguing findings were that plasma clearance, indicative of tissue uptake and utilization, was 25% greater with HMB-FA consumption compared with an equivalent HMB-CA consumption. To date, however, the majority of studies have been conducted using HMB-Ca. Figure 2 Absorbtion kinetics following ingestion of either 1 gram of calcium or free acid forms of HMB. HMB safety The safety of HMB has been widely studied [32–36]. In a study conducted in compliance with Food and Drug Administration Good Laboratory Practice, rats consuming a diet of up to 5% HMB-CA for 91 days did not exhibit any adverse effects vis a vis clinical observations, hematology, clinical chemistry or organ weights [36]. This study reported no observed adverse effect levels (NOAEL) of 3.49 and 4.16 g·kg·BM-1 for male and female rats, respectively [36]. This would be the equivalent of an 81 kg human male consuming almost 50 g HMB-Ca per day for three months with no adverse effects, based on human equivalent dosing (HED) normalized to body surface area. In humans, consumption of 6 g HMB·d-1 for one month had no effect on cholesterol, hemoglobin, white blood cells, blood glucose, liver or kidney function [33].