We found no changes in LDL cholesterol concentrations in hyperlipidemic subjects who added figs to their usual diet, compared to their usual diet alone. HDL cholesterol levels were also unchanged. The study population was a hyperlipidemic one, in which any effects of fiber in lowering LDL cholesterol would be expected to be manifest. Foods from sources like oats and barley that are high in soluble fiber significantly lower LDL cholesterol and thereby total cholesterol [4
]. However, oats and barley do not contain such large amounts of sugar per gram as figs (table ). Despite the increase in sugar intake triglyceride concentrations did not change significantly.
Comparison of food sources rich in soluble fiber (per 100 g)
We are not aware of previous studies examining the effects of dried fruit, specifically dried California Mission figs, as a source of soluble fiber to lower LDL cholesterol in hyperlipidemic adults. Our study was planned to expect an approximately 3–4% reduction in LDL cholesterol based on the amount of soluble fiber in dried California mission figs reported by Vinson [9
] in 1999. Though the study power was adequate, no effect was seen. A number of explanations may be relevant. While consuming their usual diet, subjects reported that approximately 59% of energy was from carbohydrates including almost one fourth from sugar, while <30% of energy was from fat. Compared to the general population [5
], fat intake was lower and carbohydrate intake was higher, probably reflecting the subjects’ awareness of hypercholesterolemia and attempts to limit dietary fat. Furthermore, subjects’ intake of dietary fiber was exceptionally high (mean of 29 g/day), about double of what is reported by the general population. Thus, the baseline fiber intake may have been too high for the effects of moderate amounts of added fiber to be revealed.
Serum total cholesterol levels increased in the group that began with their usual diet and crossed over to the figs-added diet, a finding that is not explained by the dietary changes observed. It is possible that the approximately 38% increase in sugar intake in the figs-added diet stimulated VLDL synthesis [11
]. It is well established that dietary carbohydrates stimulate hepatic VLDL, and simple carbohydrates have a greater stimulatory effect than complex ones [12
]. Increased VLDL may lead to increased LDL formation and thus increased total cholesterol levels, and may have counteracted the effect of fiber on lipids. In this context, it may be notable that participants had a high sugar intake already before the study.
There was no change in HDL cholesterol with fig consumption. Some data have indicated an effect of dietary fiber on increasing HDL cholesterol, but most studies indicate that HDL cholesterol concentrations are unchanged [11
]. Increased dietary carbohydrates are associated with decreased HDL cholesterol [11
]. Furthermore, the decrease in fat intake, particularly saturated fat intake, with the figs-added diet would be expected to lower HDL cholesterol. In general, study subjects reported high levels of physical activity (data not shown) and a number were recruited from the local fitness center. High levels of physical activity may counteract dietary effects on HDL cholesterol [13
The supplemented figs provided about 330 kcal/day, while the reported diet showed an increase of 187 kcal/day, indicating compensatory restriction of other foods. Over the course of 5 weeks, an increase of 6,500 kcal would be expected to be associated with a weight increase of about 0.9 kg. The observed weight change was somewhat smaller and unlikely to cause significant lipid changes.
The strengths of the study include the randomized controlled design, adequately powered number of participants and length of follow-up which was sufficient to show the tolerability of fig consumption and lipid changes. As LDL cholesterol was measured directly, we avoided the typical artefactual reduction in LDL cholesterol that is seen when the Friedewald formula is used to calculate LDL cholesterol in the presence of an increase in triglycerides. A limitation is that we were unable to obtain adequate blood samples from all subjects that completed the study. Furthermore, the subjects were free living, and assessing dietary intake in free living subjects is fraught with threats to validity, which include underreporting and biased reporting of dietary intakes [14
]. The use of repeated 24-hour recalls is increasingly recommended to avoid limitations on other methods requiring more effort on the part of the subject [15
]. Though the study was conducted within a short time period to avoid seasonal changes, such effects may have been present. The generalizability of the results to other populations is limited, as this population had a high fiber intake at baseline, were health conscious and physically active. Also, the higher soluble content of figs reported by Vinson [9
] in 1999 rather than earlier lower values [6
] was used to calculate sample size.
In conclusion, consumption of dried figs, despite the high content of soluble fiber, did not lower serum LDL or total cholesterol concentrations. Paradoxically, an increase in total cholesterol was observed in the group randomized to usual followed by figs-added diet. No increase in triglyceride concentrations or lowering of HDL cholesterol was seen despite the increase in dietary sugar.