Meal frequency and health

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Hi All,

Studies are required to be performed of the effects that meal frequency have on

our

health, says Mattson.

The need for controlled studies of the effects of meal frequency on health

Mark P Mattson

Lancet 365 (9475) 1978-1980

Only until relatively recently in human evolution have we eaten three meals

(plus

snacks) every day. Our ancestors consumed food much less frequently, and often

had

to subsist on one large meal per day or go for several days at a time without

food.1

and 2 Thus, from an evolutionary perspective, human beings were adapted to

intermittent feeding rather than to grazing. Although eating three or more meals

every day can promote rapid growth and sexual maturation in children, it might

not

be the healthiest dietary pattern for adults. Indeed, the rising tide of obesity

in

many developed countries occurs among individuals who consume several large

meals

per day. Overeating is now widely accepted as a major cause of premature death

from

cardiovascular disease, diabetes, and cancers,3 but surprisingly, few studies

have

determined how meal frequency affects health and disease risk. Nevertheless,

individuals in the health-care professions and in the lay press have repeatedly

stated that consumption of smaller and more frequent meals is healthier than

that of

larger and less frequent meals. This advice is given despite the lack of clear

scientific evidence to justify it.

Studies that have attempted to determine the effects of meal frequency on health

have resulted in mixed conclusions. For example, an early survey study4

suggested an

association between reduced meal frequency and risk factors for diabetes and

cardiovascular disease (obesity, hypercholesterolaemia, and glucose

intolerance). In

another study,5 healthy men ate either three meals or 17 small snacks every day.

After 2 weeks on these diets, participants on the snacking diet had reduced

fasting

total cholesterol, LDL cholesterol, and insulin concentrations, whereas blood

glucose and insulin responses to a glucose challenge test did not differ. Some

studies6 have shown that the omission of breakfast is unhealthy, whereas others

have

shown that this omission can reduce risk factors for cardiovascular disease and

diabetes, including elevations in concentrations of triglycerides, insulin, and

glucose.7

Different populations of people practice intermittent fasting worldwide, usually

as

part of their religion. For example, during the period of Ramadan, which lasts 1

month, Muslims do not eat during the day and typically consume most of their

food in

the evening. Analyses of blood from people before, during, and after Ramadan

have

revealed several effects of this meal-skipping diet on indicators of health and

disease risk, including increased HDL cholesterol and decreased LDL cholesterol

concentrations8 and lowered platelet aggregation,9 suggesting a reduced risk of

cardiovascular disease.

Unfortunately, the variable designs and mixed outcomes of past studies of meal

frequency and health in people have resulted in questionable and unclear

conclusions. In most instances, these studies were done over a short period,

their

sample sizes were very small (eg, and colleagues5 had seven participants

in

their study), and variables such as initial calorie intake and exercise were not

taken into account. Epidemiological studies were confounded by various

socioeconomic

and behavioural risk factors, and relied on self-reporting of food intake.

Because high calorie intake is a major risk factor for morbidity and mortality,

the

effect of meal frequency on appetite and overall calorie intake is important to

understand. In one study,10 participants ate their breakfast in either one meal

or

five small hourly meals (isocaloric). The amount of food they consumed in an

ad-libitum lunch was then measured. The single-meal group consumed a larger

lunch

than the multiple-meal group, leading the investigators to conclude that

appetite

and calorie intake is best controlled by the consumption of smaller and more

frequent meals. However, rats that were maintained on a meal-skipping diet

(alternate day feeding) consumed 30–40% less food over time than did those

allowed

to graze.11 Although several epidemiological studies have suggested an inverse

relation between meal frequency and bodyweight, a review12 of all pertinent

studies

has led to the conclusion that the epidemiological evidence represents an

artifact

and that bodyweight is determined by total calories consumed, irrespective of

meal

frequency. Therefore, how meal frequency affects overall calorie intake in

people,

and whether it varies with factors such as ethnic origin, sex, and bodyweight,

is

very important to ascertain.

By contrast with studies in people, controlled studies of the effects of meal

frequency on the function of various organ systems, incidence of disease, and

lifespan in rodents have clearly shown that diets with relatively long

inter-meal

intervals promote health and longevity. For example, mice and rats maintained on

an

intermittent fasting regimen (repeated cycles of 24 h with no food followed by

24 h

with free access to food) lived up to 30% longer than those fed ad libitum.13

and 14

Such meal-skipping diets have been shown to improve glucose regulation,15 reduce

blood pressure and enhance cardiovascular stress adaptation,11 improve renal

function during aging,16 and increase the resistance of the animals to disease

in

experimental models of cancer17 and neurodegenerative disorders.18 Especially

striking are the improved insulin sensitivity and cardiovascular risk profiles

in

animals maintained on diets with long inter-meal intervals.11 and 15

The mechanism by which meal-skipping diets improve health in rodents seems to

relate

to the induction of a beneficial type of cellular stress response, in which

genes

encoding proteins that promote cellular resistance to injury and disease are

stimulated.19 For example, concentrations of stress resistance proteins (such as

heat-shock protein 70 and glucose-regulated protein 78), and neurotrophic

factors

(such as brain-derived neurotrophic factor) are increased in brain cells of rats

and

mice maintained on meal-skipping diets. Such changes in gene expression probably

contribute to several beneficial effects of diets with reduced meal frequency.

These

effects include heightened resistance of neurons to degeneration in models of

Alzheimer's, Parkinson's, and Huntington's diseases and stroke,20, 21, 22 and 23

and

stimulation of neurogenesis, the production of new neurons from stem cells.24

Similarly, meal-skipping diets could protect against cancers by increasing the

resistance of cells to DNA damage.25 The discovery that intermittent fasting can

improve health and increase disease resistance in mice, even when overall

calorie

intake is maintained, is consistent with this stress resistance mechanism.15

The beneficial effects of diets with reduced meal frequency in rodents, which

are

striking and highly reproducible, beg the question of whether similar benefits

might

be achieved in human beings. Some aspects of studies of dietary restriction in

laboratory animals introduce at least some uncertainty as to whether reduced

calorie

and meal-skipping diets will benefit people who already have a normal or low

body-mass index. In most studies of rats and mice, controls are usually fed ad

libitum, get little exercise, and are therefore overweight. Thus, whether

meal-skipping diets will have physiological effects in people across a spectrum

of

bodyweights that are closely similar to those documented in rodents needs to be

established.

People in developed countries are increasingly presented with a bewildering

array of

diets purported to be effective in weight loss and improvement of health. In

most

instances, these diets are not effective in long-term weight reduction and even

if

they were, their effects on health would need controlled studies. One dietary

approach with a rationale similar to that of the meal-skipping diet (that has

proven

beneficial for rats and mice) has been proposed, namely, consumption of most or

all

of one's food during a 2–4 h time window every day.26 Its potential health

benefits

in people are currently being tested in a controlled study being undertaken by

investigators at the National Institute on Aging and the US Department of

Agriculture. The control group will consume three meals per day and the

experimental

group will consume their entire daily food allocation within a 4 h period in the

evening; all will be fed at bodyweight maintenance values. Participants will be

maintained on these diets for 2 months, followed by a 2 month off-diet period,

and

then another 2-month crossover on-diet period.

The fact that such a fundamental aspect of our dietary habits, the number of

meals

we eat every day, has not yet been subject to rigorous scientific investigation

is

remarkable. Until the time that clear results are obtained in well controlled

studies, specific recommendations concerning meal frequency and health are

inappropriate to make. Indeed, no clear evidence shows that the skipping of

breakfast or lunch (or both) is unhealthy, and animal data suggest quite the

opposite. However, although overeating is certainly a major health problem in

many

countries, whether dietary restriction will improve the health and longevity of

people with average or low bodyweights has not yet been established. On the

basis of

available data from studies of animals, changes in meal frequency are likely to

have

widespread effects on organ systems throughout the body. ...

Al Pater, PhD; email: old542000@...

__________________________________

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