In this 28-day study of moderately obese persons, both the RM and PFS LCD effectively promoted significant weight loss (Table 1). Caloric intake of the two groups differed by 68 Kcal/day. No significant difference in total weight loss was observed between the RM and PFS groups, -5.26 ± 0.84 and -5.74 ± 0.63 kg, respectively. Weight loss experienced by the RM and PFS groups in the current study was comparable to that observed on week four of other previous LCD studies [12, 13, 29, 30].
The carbohydrate intake for both the RM and PFS groups was 17 ± 3.6 and 18 ± 2.5% of total calories, respectively, and significantly lower than the current USDA recommendation of 45–65% . The degree of carbohydrate restriction in the current study was similar to some previous studies [9, 12] but greater than others [7, 8, 10, 13, 30] and greater than the target value of the Atkins induction phase .
Persons consuming the PFS diet had a significantly greater PUFA intake than those in the RM group (p = 0.036), although the difference in specific n-3 and n-6 PUFAs for the diets was not calculated. The SFA intake of the RM group was slightly elevated, relative to the PFS group. Persons in the RM group had a mean intake of SFA that was 32.42 ± 4.62 g/day and the SFA intake of the PFS group was 25.12 ± 2.01 g/day, this difference approached significance (p = 0.137). In interviews with subjects prior to the start of the study, it was determined that cheese was a major element that subjects in both the RM and PFS groups strongly preferred to include in their diets. The investigators chose to permit controlled and documented cheese consumption in the PFS group in order to improve honest dietary reporting and compliance. In light of the high SFA content of cheese, it was not surprising that the difference between the two groups for SFA intake only approached significance.
The day 28 plasma fatty acid profile of EPA, DHA, and DPA suggests that the RM and PFS groups were compliant with regards to consuming their assigned diets (Table 3). Two specific PUFAs that are indicative of PFS consumption are the n-3 marine oils EPA and DHA [21, 31]. Plasma fatty acid levels of EPA and DHA in the PFS group were both greater than that observed in the RM group. The differences approached significance with p-values of 0.170 and 0.095 for EPA and DHA, respectively. Subjects consuming the RM diet, which typically contained beef products, would be expected to consume more of the non-marine n-3 fatty acid DPA  and stearic acid [16, 18]. The group-specific difference for DPA was significant (p = 0.051) and approached significance for stearic acid (p = 0.071). Figure 2 demonstrates that within the RM and PFS groups, when expressed as a percentage of the total, plasma palmitic or stearic acid was not tightly correlated with total SFA intake, suggesting that the control of the plasma levels of these two fatty acids is under predominately metabolic, not dietary control.
The PFS diet resulted in the consumption of nearly twice the cholesterol (630 ± 95 mg/day) as members of the RM group (333 ± 39 mg/day). This high cholesterol intake was mostly attributable to shrimp and eggs consumed on 25 and 88% of all days, respectively. Subjects made these cholesterol-rich foods a staple of their self-purchased free-living diets because of taste preferences, familiarity, and product availability. Studies of human egg and shellfish consumption have suggested that cholesterol content has, at best, only a small impact on the plasma cholesterol profile [33–35]. Consumption of large amounts of cholesterol-rich eggs and shrimp by PFS subjects may have influenced the expected improvements in the plasma lipid profile that would be expected to accompany the observed weight loss [9, 36]. The moderate degree of carbohydrate restriction observed in the current study may have been inadequate to produce the LCD induced changes in the plasma cholesterol profile associated with the previously described studies.
Subjects experienced a significant reduction in plasma triglycerides in the PFS group (p = 0.042) while plasma triglyceride reduction in the RM group was not significant (p = 0.326). Because the RM subjects began the study with a plasma TG concentration that was generally lower than that of the PFS group they may have been less responsive to diet induced reductions in plasma triglycerides.
The total daily fiber intake recommendation of the Food and Nutrition Board is 38 and 25 g/day for men and women . In the current study, fiber intake for RM and PFS subjects was 6.4 ± 1.1 and 6.5 ± 0.8 g fiber/day, respectively. It has been previously demonstrated that increased fiber intake as part of a LCD may improve potential reductions in LDL cholesterol, though it is not required for improvements in the plasma lipid profile .