Gastric Emptying For Specific Foods May Be A Key To
Managing Deadly Illnesses In The Elderly
April 18, 2003 (Bethesda, MD) -- The rate of
gastric emptying is a major measure of the glucose and cardiovascular
responses to oral carbohydrates. The former is key to the dietary
management of people with diabetes mellitus, in whom strict control of blood
glucose has been shown to reduce microvascular complications. As
cardiovascular responses are relevant to the prevention of postprandial
hypotension (subnormal arterial blood pressure following a meal), this can
be an important clinical problem. Both Type 2 diabetes and postprandial
hypotension occur most frequently in the elderly.
Now, a team of Australian physiologists has produced
evidence that the gastric emptying, or nutrient absorption, for specific
foods, may hold the answer for dietary management of deadly illnesses
affecting the elderly population.
Background
An individual’s blood glucose levels after eating are
influenced by a number of factors but it is now recognized that gastric
emptying accounts for at least 35 percent of the variance in peak
postprandial glucose levels after oral glucose (75 grams) in both healthy
individuals and patients with Type 2 diabetes. Controlling gastric emptying
by dietary and pharmacological means in order to minimize postprandial
glucose represents a new approach to glycemic control. Studies in rodents
have established the importance of early insulin release in the control of
postprandial glucose excursions in that a small, early increase in
blood/portal insulin levels is more effective than a larger, later increase
in reducing blood glucose levels. Thus, whereas slowing of nutrient
absorption may benefit Type 2 diabetes patients, it is possible that modest
acceleration of the initial gastric emptying rate of carbohydrates would
have a beneficial effect on overall glycemia in Type 2 diabetes. This would
also be true among healthy subjects because it would to an increase in early
insulin release, particularly if the subsequent emptying of carbohydrates is
slower.
Postprandial hypotension, defined as a fall in systolic
blood pressure of approximately 20 mmHg after a meal, occurs frequently in
older persons and in patients with diabetes mellitus and autonomic
neuropathy and is associated with a number of clinical conditions including
loss of consciousness, falls, stroke, angina, and increased mortality.
Ingestion of a carbohydrate, particularly large amounts, induces the
greatest cardiovascular response, particularly after a meal while fat,
protein, or water have relatively little effect.
The mechanisms mediating the fall in postprandial blood
pressure are poorly defined. It is believed that digestive blood flow,
release of gut hormones, and sympathetic nervous activity are thought to
play a role. Recent studies indicate that the magnitude of the fall in blood
pressure in both Type 2 diabetes and healthy older subjects is greater when
gastric emptying is relatively more rapid. Furthermore, in healthy older
subjects, the fall in blood pressure and increase in heart rate are greater
during intraduodenal glucose infusion. These observations suggest that the
postprandial fall in blood pressure and rise in heart rate may be related to
the early phase of gastric emptying.
A New Study
The aims of a new study were to evaluate the effects of
ingestion of a solid, noncarbohydrate meal on gastric emptying and
intragastric distribution of, and the glycemic and cardiovascular responses
to, a liquid glucose load in healthy, older subjects. The study objective
was to assess whether a solid meal would accelerate the initial emptying
phase and intragastric distribution of a liquid leading to (1) an overall
reduction in postprandial glycemia consequent to an increase in early
insulin secretion and (2) a greater postprandial fall in blood pressure and
increase in heart rate.
The authors of “Solid Meal on Gastric Emptying of, and
Glycemic and Cardiovascular Responses to, Liquid Glucose in Older Subjects,”
are Melanie K. Berry, Antonietta Russo, Judith M. Wishart, Anne Tonkin,
Michael Horowitz, and Karen L. Jones, all from the University of Adelaide,
Royal Adelaide Hospital, Adelaide, South Australia, Australia. Their
findings appear in the April 2003 edition of the American Journal of
Physiology—Gastrointestinal and Liver Physiology, one of 14 journals
published monthly by the American Physiological Society (APS).
Methodology
Twelve healthy older subjects (six male, six female),
age 72.9 + 2.1 years; body mass index (BMI) 25.3 + 0.5 kg/m2,
were enrolled in the study. Each subject underwent concurrent measurements
of gastric emptying, blood glucose, serum insulin, blood pressure, and heart
rate on two days separated by at least three days. After exclusions, ten
subjects were studied. Each subject had measurements of gastric emptying,
blood glucose, serum insulin, blood pressure, and heart rate after ingestion
of a glucose drink with (mixed meal) or without (liquid only) a solid
meal.. None of the research subjects had evidence of postprandial
hypotension or cardiovascular autonomic neuropathy.
Results
Gastric emptying of liquid was initially slightly more
rapid after the mixed meal compared with liquid only at five minutes and
much slower after 120 minutes. The time to peak blood glucose was less and
blood glucose subsequently lower after the mixed meal. The increase in serum
insulin was greater after the mixed meal. Blood pressure fell in the first
30 min, with no difference between the two meals. Increase in heart rate
after both meals was greater after the mixed meal.
The results also revealed:
-
the presence of a 300-g noncarbohydrate solid meal has
discrepant effects on early and subsequent emptying of a nutrient liquid
meal, so that gastric emptying of a 50-g glucose drink is initially
slightly faster and then much slower compared with when the liquid is
consumed alone;
-
acceleration of the early liquid emptying induced by the
solid meal is associated with a change in intragastric distribution, so
that relatively more liquid is retained in the distal stomach;
-
the more rapid, early emptying of glucose is associated with
an earlier peak in blood glucose, a greater serum insulin response, and an
overall reduction in postprandial glycemia; and
-
whereas the initial postprandial fall in blood pressure was
not affected by the presence of a solid meal, the increase in heart rate
was greater.
Conclusions
These observations are consistent with the concept that
the early phase of gastric emptying is a major determinant of postprandial
glycemia as well as the cardiovascular response to a meal and have
implications for the dietary management of Type 2 diabetes and postprandial
hypotension.
Although the subjects were healthy volunteers, the
observations are consistent with evidence that modulation of gastric
emptying by dietary or pharmacological means could be used to optimize blood
glucose control in Type 2 diabetes. The novel concept presented is that
dietary strategies should be directed at the stimulation of a greater
initial insulin response by accelerating the early emptying of carbohydrates
and, subsequently, slowing it to delay glucose absorption. Studies in
patients with Type 2 diabetes are required to evaluate this further,
however.
The findings also indicate that in healthy older
subjects, the rate of delivery of glucose to the small intestine is a
determinant of the postprandial fall in blood pressure and increase in heart
rate. In this research, the initial fall in blood pressure after an oral
glucose load was not affected by a solid meal, whereas it may have been
expected that more rapid, early liquid emptying would induce a greater fall
in blood pressure. It appears that the initial absorption rate of glucose is
a fundamental determinant of the cardiovascular response to carbohydrate,
although the mechanisms mediating these effects remain uncertain.
Accordingly, dietary strategies for the prevention of postprandial
hypotension should perhaps focus on delaying the initial gastric emptying
and/or small intestinal absorption of carbohydrate. Studies are now required
to address these hypotheses.
Source: April 2003, edition of the American
Journal of Physiology—Gastrointestinal and Liver Physiology, one of 14
journals published monthly by the American Physiological Society (APS).
-end-
The American Physiological
Society (APS) was founded in 1887 to foster basic and applied science, much
of it relating to human health. The Bethesda, MD-based Society has more than
10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals
every year.
***
Editor’s Note: A copy of the research article is
available in pdf format to the press. Members of the press are invited to
obtain a pdf copy of the study and to interview members of the research
team. To do so, please contact Donna Krupa at 703.527.7357 (direct dial),
703.967.2751 (cell) or djkrupa1@aol.com.
