Effects of timing of hypercaloric snacking diets on metabolism and brain

Food intake has dramatically changed in the last decades and hypercaloric
diets, sugar-sweetened beverages and snacking behaviour have all been
associated with an increase of body weight and diabetes. Specific brain
regions, including the hypothalamus and reward areas, strongly regulate feeding
behaviour. Besides these regions, the circadian clock, located in the nucleus
suprachiasmaticus (SCN) are involved in the regulation of food intake, glucose
and fat metabolism in rodents and humans. The timing of food intake is an
important external synchronizer and alterations in feeding behaviour, such as
skipping breakfast, irregular meal pattern and snacking, may lead to
disturbances of the circadian rhythm of metabolism and thereby contribute to
obesity and insulin resistance. Cerebral serotonin is involved in food intake
and regulation of body weight. Extracellular serotonin concentration, available
for receptor binding and serotonin signalling, is regulated by the serotonin
transporter (SERT). Serotonergic transmission and SCN physiology are strongly
intertwined. SERT shows a diurnal rhythm in mice with higher expression and
activity during the dark (active) phase. Moreover key signaling molecules from
the serotonin signaling network, such as SERT and different serotonin receptors
such as the 5-HT1B, 5-HT7, and 5-HT2C receptors are expressed in the SCN
biological clock nucleus. Interestingly, we and others recently found a
negative association with diencephalic SERT and body weight and a positive
correlation between SERT and insulin sensitivity . Moreover, we recently found
a decrease in diencephalic SERT upon a 6 weeks high fat high sugar (HFHS)
snacking diet in lean men.
We therefore hypothesize that a hypercaloric HFHS snacking diet through
manipulation of midbrain serotonin signalling influences metabolic rhythmicity
in the SCN, which contributes to a reduction in insulin sensitivity in humans.
Furthermore, shifting the snacking to inappropriate time points, i.e. during
the dark phase, will more profoundly affect metabolism due to more severe
misalignment.

To determine the effects of hypercaloric HFHS snacking in the morning or
evening on insulin sensitivity and serotonin function in the diencephalon.

Open randomised controlled intervention study

Subjects will consume a 60% surplus hypercaloric diet composed of a
self-selected, eucaloric healthy ad libitum diet plus a HFHS drink five times a
day either before 11:30 (group 1) or after 19:30 (group 2). After the
intervention of 4 weeks, subjects will follow a hypocaloric diet to lose the
gained weight.

Total study duration is 8 weeks. Subjects will visit the AMC weekly and total
visit time will be about 30 hours. At study entry, subjects will be screened
for in- and exclusion criteria. Participations will follow a hypercaloric HFHS
diet for four weeks after randomization. The hypercaloric diet will be based on
a 60% caloric surplus on top of their ad libitum diet which will result in a
modest weight gain. After the hypercaloric phase, a hypocaloric diet will
follow to lose the gained weight under strict supervision. Temporary weight
gain does not provoke serious health risks.
Before and after four weeks on the hypercaloric diet, a 2-step hyperinsulinemic
euglycemic clamp will be performed using stable isotopes. Stable isotopes
behave like their natural substrates and are therefore not harmful. Blood
samples will be obtained from an intravenous cannula in a peripheral arm vein.
Hypoglycemia during the hyperinsulinemic clamps will not occur because plasma
glucose will be measured bedside at regular intervals. Total clamping time on
one day will be 7 hours.
Subjects will undergo a SPECT-scan with the radioligand [123I]FP-CIT,
administered intravenously. At 2 and 3 hours after administration, a SPECT-scan
of the brain will be performed which takes about 40 minutes each, during which
the participant lies down on his back on the gamma camera bed. The day before
SPECT-scan and on the morning of the scan, subjects will be given potassium
iodide tablets to reduce uptake of the radioligand in the thyroid. [123I]FP-CIT
has a European (CPMP) registration, and it has been shown that it has no
serious side effects. As the dose equivalent per [123I]FP-CIT injection amounts
to 2.7 mSv (111MBq), the total dose equivalent of the participating subjects
will amount less than 10.0 mSv (222 MBq) (WHO category IIb). A pharmacological
MRI will be performed following serotonin challenge with a single and low dose
of the selective serotonin reuptake inhibitor (SSRI) citalopram (7.5mg
intravenously) to evaluate the serotonergic system. ASL is a non-invasive
cerebral blood flow imaging modality that uses magnetically labelled blood
water protons as an endogenous tracer of cerebral blood flow. Citalopram is the
only SSRI registered in the European Union for intravenous administration and a
well-tolerated treatment for severely depressed patients and for serotonin
modulation in MRI. For careful analysis of the SPECT-scan, a structural MRI of
the brain will be performed. In addition an MRI of the abdomen will be
performed to quantify visceral- and liver fat. The MRI-scans requires lying as
quiet as possible for 75 minutes.