Are dieting-related cognitive impairments a function of iron status?

Abstract

The aim of the present study was to investigate whether the impairments in cognitive function observed in unsupported dieting are related to compromised Fe status. During a non-clinical intervention, overweight participants (age: 18 -45 years, BMI: 25-30 kg/m 2 ) either participated in a commercially available weight-loss regimen (n 14), dieted without support (n 17) or acted as a non-dieting control group (n 14) for a period of 8 weeks. Measurements of cognitive function and blood chemistry were taken at a pre-diet baseline, after 1 week and 8 weeks of dieting. After 1 week, unsupported dieters displayed impaired verbal memory, executive function and slower reaction speeds than the other two groups, this difference disappearing by the end of the study. There were no significant group-related changes in blood chemistry over the course of the study, although there were group-related changes in a number of self-reported food-related cognitions. In conclusion, impaired cognition among unsupported dieters is not due to compromised Fe status and is most likely to result from psychological variables. Key words: Dieting: Dietary support: Cognition: Iron metabolismDeliberate restriction of food intake to control weight is one of the most common food choice-related behaviour in the developed world. Indeed, over one-third of the general US population is classed as obese (1) , with an associated impact on health treatment resources (2) . Within the context of these rising obesity rates (3) , an understanding of the psychological impact of undernutrition and weight loss assumes an increasing importance.While there are undoubted health benefits of controlling obesity, the attempt to lose weight by dieting has been associated with a number of negative psychological consequences such as increased depression and low self-esteem (4) . Although the evidence concerning the psychological effects of experimentally induced weight loss is equivocal (5) , evidence suggests that dieting is reliably associated with a range of impairments in cognitive function. For instance, dieting has been associated with slower reaction speed, impaired verbal memory and an impaired ability to sustain attention (6,7) . A number of studies have indicated that this pattern of impaired task performance is primarily due to a reduction in available working memory capacity (8 -11) , which is primarily due to preoccupying cognitions relating to hunger (8) and body shape-related self-esteem (12,13) . This is important, since working memory is the primary cognitive domain, controlling moment-to-moment rules of action, planning ability and the short-term retention of information. The most commonly accepted model of working memory (14) proposes a tripartite system comprising a phonological loop (controlling verbal short-term memory), a visuospatial sketchpad (controlling visual memory) and an overarching supervisory system known as the 'central executive'.It has also been found that the way in which weight loss is attempted influences cognitive function, ...

Weight loss is associated with improvements in cognitive function among overweight and obese people: A systematic review and meta-analysis

“…After excluding 1,209 papers on the grounds of a review of their titles and abstracts, 41 full-text articles were examined, and 20 studies were ultimately included in our meta-analysis (Figure 1) Boraxbekk et al, 2015;Brinkworth et al, 2009;Bryan and Tiggemann, 2001;Buffenstein et al, 2000;Cheatham et al, 2009;Green and Elliman, 2012;Guldstrand et al, 2003;Halyburton et al, 2007;Kretsch et al, 1997;Marques et al, 2014;Martin et al, 2009;Miller et al, 2013;Napoli et al, 2014;Prehn et al, 2016;Siervo et al, 2012;Smith et al, 2010;Spitznagel et al, 2014;Wing et al, 1995;Witte et al, 2009). …”

“…The 13 longitudinal studies Boraxbekk et al, 2015;Brinkworth et al, 2009;Buffenstein et al, 2000;Cheatham et al, 2009;Guldstrand et al, 2003;Halyburton et al, 2007;Kretsch et al, 1997;Marques et al, 2014;Miller et al, 2013;Siervo et al, 2012;Spitznagel et al, 2014;Wing et al, 1995) included 551 participants, while the 7 RCTs (Bryan and Tiggemann, 2001;Green and Elliman, 2012;Martin et al, 2009;Napoli et al, 2014;Prehn et al, 2016;Smith et al, 2010;Witte et al, 2009) encompassed 468 individuals (328 in the treated groups and 140 controls), representing a total of 1,019 participants with obesity or being overweight at baseline. The mean age was 50.0 (standard deviation, SD=10.7) years, and the included participants were predominantly women (=78.3%).…”

“…As shown in Supplementary Table 2, the seven RCTs (Bryan and Tiggemann, 2001;Green and Elliman, 2012;Martin et al, 2009;Napoli et al, 2014;Prehn et al, 2016;Smith et al, 2010;Witte et al, 2009) included 328 participants randomized to treated groups (262 in a dietary intervention group, 26 treated with physical activity, and 40 with both interventions).…”

“…Regarding quality, using the Jadad's scale for this evaluation, one study reported 3 points over 3 available, one only one point and the others 2 points. Taking the controls as reference, four studies (Bryan and Tiggemann, 2001;Green and Elliman, 2012;Prehn et al, 2016;Napoli et al, 2014) reported a significant improvement in attention parameters in the treated group (222 treated vs. 104 controls; SMD=0.44; 95%CI: 0.26-0.62, p<0.0001; I 2 =60%) ( Table 2). However, only physical activity alone, and diet and physical activity together, were able to improve these outcomes in one study (Napoli et al, 2014).…”

“…Treated participants showed significant improvements in memory tests (Bryan and Tiggemann, 2001;Green and Elliman, 2012;Martin et al, 2009;Smith et al, 2010;Witte et al, 2009) (236 treated vs. 113 controls; SMD=0.35; 95%CI: 0.12-0.57, p=0.002; I 2 =64%), particularly when diet and calorie restriction were used (204 treated vs. 113 controls; SMD=0.37; 95%CI: 0.09-0.35, p=0.01; I 2 =71%). This outcome, however, seemed to be affected by publication bias (Egger's test=3.72±0.68;p=0.004), likely due to the inclusion of studies reporting negative findings.…”