Recently, interoception and homeostasis have been described in terms of predictive coding and active inference. Afferent signals update prior predictions about the state of the body, and stimulate the autonomic mediation of homeostasis. Performance on tests of interoceptive accuracy (IAc) may indicate an individual's ability to assign precision to interoceptive signals, thus determining the relative influence of ascending signals and the descending prior predictions. Accordingly, individuals with high IAc should be better able to regulate during the postprandial period. One hundred females were allocated to consume glucose, an artificially sweetened drink, water or no drink. Before, and 30 min after a drink, IAc, heart rate (HR) and blood glucose (BG) were measured, and participants rated their hunger, thirst and mood. A higher IAc was related to lower BG levels, a decline in anxiety and a higher HR, after consuming glucose. A higher IAc also resulted in a larger decline in hunger if they consumed either glucose or sucralose. These data support the role of active inference in interoception and homeostasis, and suggest that the ability to attend to interoceptive signals may be critical to the maintenance of physical and emotional health.
Those with disordered eating and/or obesity often express difficulties in sensing or interpreting what is happening in the body (interoception). However, research is hindered by conceptual confusion, concerns surrounding domain specificity, and an inability to distinguish sensory (bottom-up) and expectation driven (top-down) interoceptive processes. A paradigm was therefore developed from an active inference perspective. Novel indices were computed and examined in those with alexithymia: a personality associated with interoceptive deficits and disordered eating. The paradigm successfully identified individuals driven by sensations rather than expectations: alexithymia was characterized by attenuated prior precision (a larger divergence between pre-prandial and post-prandial satiety, and low expectation confidence), and increased prediction error (a higher correlation between changes in hunger and blood glucose, and greater rebound hunger after a sensory incongruent drink). In addition, those with a higher BMI were less confident and had a larger anticipated satiety divergence. These findings demonstrate the need to move beyond existing paradigms such as the Satiety Quotient and Heartbeat Counting Task which may have limited our understanding of eating behaviour.
Sleep problems are extremely common in industrialized countries and the possibility that diet might be used to improve sleep has been considered. The topic has been reviewed many times, resulting in the frequent suggestion that carbohydrate increases the uptake of tryptophan by the brain, where it is metabolized into serotonin and melatonin, with the suggestion that this improves sleep. An alternative mechanism was proposed based on animal literature that has been largely ignored by those considering diet and sleep. The hypothesis was that, as in the hypothalamus there are glucose-sensing neurons associated with the sleep-wake cycle, we should consider the impact of carbohydrate-induced changes in the level of blood glucose. A meta-analysis found that after consuming a lower amount of carbohydrate, more time was spent in slow-wave sleep (SWS) and less in rapid-eye-movement sleep. As the credibility of alternative mechanisms has tended not to have been critically evaluated, they were considered by examining their biochemical, nutritional, and pharmacological plausibility. Although high carbohydrate consumption can increase the uptake of tryptophan by the brain, it only occurs with such low levels of protein that the mechanism is not relevant to a normal diet. After entering the brain tryptophan is converted to serotonin, a neurotransmitter known to influence so many different aspects of sleep and wakefulness, that it is not reasonable to expect a uniform improvement in sleep. Some serotonin is converted to melatonin, although the exogenous dose of melatonin needed to influence sleep cannot be credibly provided by the diet. This review was registered in the International Prospective Register of Systematic Reviews (CRD42020223560).
Objectives The study examined the long-term effects of a botanical supplement containing cinnamon, turmeric/curcumin, chromium and alpha-lipoic acid on blood glucose (BG), blood lipids and cognitive measures of healthy, older adults. Methods Healthy, older adults aged 51 to 79 years (N = 30, 16 females, 14 males) were randomized to consume either 4 tablets/day of the active dietary supplement (1400 mg blend of cinnamon [Cinnamomum cassia bark extract], curcumin, turmeric [Curcumin Longa L. root extract and powder]; chromium and alpha-lipoic acid) or a placebo for three months in a double-blind between-subjects trial. At monthly intervals participants completed a 3.0-hour oral glucose tolerance test (OGTT). BG and blood lipids were measured at baseline and half-hour intervals, and subjects performed a battery of cognitive tests. Results After the two- and three-month time point there was a trend for a greater fall in BG in those taking the supplement. However, at completion of the study there were no statistically significant overall effects of supplementation on either BG levels or hemoglobin A1c. There was a positive effect of the supplement on total cholesterol and for individuals who had poorer glucose control (F(1, 16) = 12.86, P < 0.002). Results from the cognitive assessments indicated significant differences in word recall for the participants consuming the active dietary supplement (F(1, 26) = 5.74, P < 0.02). Measures of focused attention revealed significant improvements in reaction times in the group receiving the supplement (F(1, 26) = 4.48, P < 0.04). Conclusions These findings suggest that the chronic ingestion of a dietary supplement containing cinnamon and curcumin/turmeric extracts, chromium and alpha-lipoic acid positively impacts blood lipids as well as aspects of cognitive performance in healthy individuals assessed during an OGTT. Funding Sources NeoLife International, LLC, Fremont, CA, USA.
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