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.

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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.

Objectives Carbohydrate is the nutrient most commonly said to influence sleep: it is proposed that a high intake increases the uptake of tryptophan by the brain, where it is metabolized into serotonin and melatonin. As this mechanism depends on the relative amount of carbohydrate and protein, studies were reviewed where diets differed in these macro-nutrients. Methods The Web of Science and Medline were interrogated using terms related to carbohydrate and sleep. Papers were retained if two diets, differing in the percentage of calories coming from carbohydrate, had been contrasted using either polysomnography or actigraphy. Measures considered with polysomnography included sleep onset time; sleep efficiency; rapid eye-movement (REM) and slow wave sleep (SWS). Measures examined from actigraphy included: sleep efficiency; duration of sleep. Meta-analysis was conducted using Review Manager 5.2 (Cochrane) using a random-effects model. Results With the polysomnography measures six studies met the inclusion criteria. A lesser consumption of carbohydrate was associated with more SWS (SMD = 0.47; CI 0.06 – 0.88; P = 0.02; I2 = 0%) and less REM (SMD = – 0.47, CI –0.87– –0.07, P = 0.02, I2 = 0%). A lower intake of carbohydrate was also associated with a shorter time before falling asleep (P = 0.03; I2 0%). Sleep efficiency is the percentage of time spent asleep, relative to the total time in bed. Using polysomnography there was a trend for better sleep efficiency to be associated with with a lower intake of carbohydrate, although it just missed significance (P = 0.06). However, using actigraphy those eating less carbohydrate were more sleep efficient (SMD = 1.25; CI 0.35 – 2.15; P = 0.007; I2 = 0%). Conclusions No study had the high level of carbohydrate needed to raise tryptophan; rather studies had enough protein to reduce the uptake of tryptophan. A novel possibility is that blood glucose levels modulate sleep. Glucose metabolism varies; it is less during SWS and greater with REM. There are many reports associating the nature of sleep with glucose tolerance. As several hormones control glucose levels, some stimulated by the level of glucose, there is a need to consider diet hormonal interactions. As SWS is believed to be restorative and aid plasticity, increasing SWS with lower carbohydrate have may functional implications. Funding Sources No external funding.

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Objectives A systematic review and meta-analysis compared the effects of high (HGL) and low glycemic load (LGL) breakfasts on the cognitive performance of adults. In particular, the time after eating that cognition was assessed and the influence of pre-existing glucose tolerance (GT) were considered. Methods A systematic search for randomized and non-randomized acute breakfast studies was conducted using PubMed, Scopus, and Cochrane Library. Data were available from 15 studies (1,100 participants, age 20–80 years). Episodic memory (e.g., word list recall), working memory (e.g., Serial Sevens), and attention/vigilance (e.g., Trails Part A) were examined. Better and poorer GT were defined as fasting glucose < or > 6.1 mmol/L (110 mg/dL) and/or two-hour postprandial glucose < or > 7 mmol/L (126 mg/dL). All analyses were performed using RevMan 5.3 (Cochrane) and a random-effects model. Results Five to 110 minutes after eating a HGL or LGL breakfast there were no differences cognition. However, between 120 and 195 minutes, immediate episodic memory was significantly better following a LGL breakfast (SMD = 0.16, 95% confidence interval [CI] = –0.00–0.32, P = 0.05, I2 = 0%). Pre-existing glucose tolerance (GT) status moderated this effect. In those with better GT, immediate episodic memory was significantly better following a LGL breakfast (SMD = 0.26, 95% CI = 0.00–0.52, P = 0.05, I2 = 0%), whereas there was no difference in those with poorer GT (SMD = 0.12, 95% CI = –0.21–0.45, P = 0.47, I2 = 0%). Conclusions A LGL breakfast improved memory later in the morning, especially in those with better GT. The phenomenon is unlikely to occur in pre-diabetics or type 2 diabetics and as such there are no clinical implications. There is, however, a possibility of exploring the nature of breakfast, or developing functional foods, to improve memory and work performance. If a similar phenomenon was found in children, there could be positive consequences for school performance. Funding Sources This study was not funded.