Few people are surprised when
told that it is relatively hard to lose
weight in the fall heading into winter
and relatively easy to lose weight in
the spring. This is not just a matter
of Thanksgiving, Christmas, New
Year’s and the Super Bowl, although
the grouping of these holidays hardly helps. Our
bodies exhibit metabolic changes in preparation
for the winter months and then tend to reverse
at least some of these changes as the next year
progresses. Hibernation is the classic example
of these changes, but seasonal fluctuations in
metabolism are shared by a quite large proportion
of all mammals in temperate climates, including
humans. More surprising to most of us is the fact
that similar fluctuations in energy use and storage
are tied to the twenty-four hour (circadian) cycle,
as well, and these fluctuations are so strong that
they may be more important than the usual dietary
suspects — the amounts of carbohydrate, fat and
protein in the diet — that typically are the targets of
dietary advice.
The Day/Night Cycle Exists Even For Genes
A few years ago, a team of researchers experimented
to learn if circadian rhythmic patterns apply to
human fat tissue.1 In this particular case, they
wanted to know if genes related to cortisol
metabolism exhibited such rhythms in adipose
tissue. (Cortisol is sometimes called the “fight or
flight” hormone; it also plays a large role in weight
gain.) Sure enough, the scientists found rhythmicity
in cells from both men and women and in fat cells
both from under the skin (subcutaneous) and
around the abdomen (visceral deposits), with the
amplitude of the circadian rhythmicity being greater
in the visceral fat tissue genes.
Yet another circadian pattern involving cortisol
is important for weight gain in those under mild
chronic stress, including the stress associated with
diabetes. Under normal circumstances, the body
tends to have a period of time during inactivity — our
sleep cycle — in which cortisol levels in the blood
exhibit a prolonged “trough” of reduced presence.
Mild stress may only slightly elevate the total
daily glucocorticoid level, yet still alter the way in which tissue receptors respond. In an animal model, healthy
animals after several days of added glucocorticoid (via pellets
under the skin) showed reduced adrenal and thymus weight,
i.e., adrenal exhaustion and reduced immune response, and
elevated insulin levels.2 This would seem to be similar to
early stage Metabolic Syndrome as the animals struggle to
regulate the excess sugar being released into the system by
the glucocorticoid. In diabetic animals, insulin levels drop
dramatically with continued glucocorticoid challenge, which
means that the ability to regulate blood sugar also drops.
Conversely, food intake and blood triglycerides increase in
diabetic animals versus controls. Chronic exposure to cold
in this model has the same type of effect as does added
glucocorticoid, including the same disruption of the circadian
rhythm of reduced glucocorticoid during the rest period. As
the authors of this study observe, “studies in man suggest
that perceived chronic stress also flattens the amplitude of
the circadian cortisol rhythm by elevating trough and reducing
peak levels; subjects who reported increased stress were
abdominally obese, hyperinsulinemic and hypertensive.”
With the foregoing evidence in mind, it is easy to grasp that
activities such as exercise and meal timing may play significant
roles in body weight and health. Hunger levels, the ability to
dispose of meal calories and the degree of metabolic response,
including metabolizing excess calories, all respond to stress
levels and the timing of activities.
Calorie Storage Depends On Meal Times
It has been known for several decades that the composition of
the initial meal of the day tends to set the body’s response to
food intake later in the day. Not eating breakfast, for instance,
tells the body that it should reduce energy expenditures and
conserve in the face of famine conditions. Eating refined
carbohydrates and sugars causes an insulin release that blocks
fat metabolism, forces the body to rely on stored glycogen
for energy and leads to energy peaks and valleys, the blood
sugar “roller coaster.” Protein breakfasts including either fat or
carbohydrates tend to even out energy levels and retain what
is known as “metabolic flexibility,” the ability to harness either
glucose or stored fat for fuel as needed.
A good example of the meaning of meal timing in practice
emerged recently in several trials using animal models. Mice
and rats are extremely sensitive to the level of fat in their diets,
in part because their natural diets are very low in fats. Unlike
humans, both animals eat more or less continuously during
their waking periods of activity. Either high- or low-fat diets
spread throughout their normal 12-hour feeding period exercise
limited effects on food intake and energy usage. Under these
conditions, the animals generally adjust consumption and
expenditure to maintain balance and metabolic parameters
within normal ranges. Feeding a high-fat meal at the beginning
of the feeding period does not alter metabolic flexibility and,
again, the animals adjust. However, the same high fat meal
taken at the end of the animals’ waking period leads to increased
“weight gain, adiposity, glucose intolerance, hyperinsulinemia,
hypertriglyceridemia, and hyperleptinemia” independent of
either total or fat-derived calories.3 The major surprise, one
that runs counter to common assumptions, is this finding: “We
report that high fat feeding at the transition from sleeping to
waking appears to be critically important in enabling metabolic
flexibility and adaptation to high carbohydrate meals presented
at later time points. Conversely, high carbohydrate feeding at
the beginning of the waking period dramatically impairs the
metabolic plasticity required for responding appropriately to
high fat meals presented at the end of the waking period.” In
other words, the standard American breakfast of sweetened
cereal or other refined carbohydrate products impairs the ability
of the body to properly metabolize fats eaten later in the day.
Other researchers have found similar results. Again in a
mouse model, one group found that a diet sufficiently high
in fat to induce weight gain and related changes if fed ad
libitum did not lead to such changes if restricted to a limited
feeding period.4 Not caloric restriction or fat restriction, but
a restricted feeding period led to favorable results. “Timed
restricted feeding provides a time cue and resets the circadian
clock, leading to better health.” Simply put, a timed high-fat
diet resets circadian metabolism and prevents obesity in this
mouse model despite the high-fat content in an animal that
normally consumes very little fat.
What About Humans?
A number of recent clinical experiments have confirmed the
findings from these animal models as being applicable to
humans, with increased protein consumption at breakfast
proving to be especially helpful. For instance, in overweight/
obese, “breakfast-skipping” late-adolescent girls, breakfast,
and especially a high protein breakfast led to better appetite
control, better regulation of food intake and reduced evening
snacking compared to not eating breakfast even though in this
short study (one week) there was no change in total energy
intake.5
Another study, this one in overweight and obese adults,
found that both a low-carbohydrate breakfast (not specifically
high in protein) and a high-protein plus carbohydrate breakfast led to impressive weight loss over a period of 16 weeks (15.1±1.9kg and 13.5±2.3 kg, respectively) when followed in conjunction
with reduced energy intake. After the diet ended, subjects
were tracked for a further 16 weeks. As is found commonly in
such models, there was significant weight regain in the lowcarbohydrate
only breakfast group compared to the protein
plus carbohydrate arm.6 This finding should surprise no one in
that it is easier to add protein to more “normal” meal patterns
than it is to radically reduce carbohydrates. Low-carbohydrate
diets tend to lead to considerable rebound as dieters return
to their normal eating habits. People who have increased their
protein consumption along with changing other eating habits
find it easier to continue some version of their new eating
pattern.
Yet another study, this one restricted to overweight and
obese women, found that in a restricted calorie diet (~1,400
kcal) the results were significantly better at the end of 12 weeks
in the women who ate a large breakfast (700 kcal breakfast,
500 kcal lunch, 200 kcal dinner) as opposed to a large dinner
(200 kcal breakfast, 500 kcal lunch, 700 kcal dinner).7
Eating breakfast, especially one that is higher in protein,
has been found again and again to be superior to skipping
breakfast or eating a breakfast built around carbohydrates. The
shake out in meal composition revolves much more around the
role of protein than fat because fats actually play a somewhat
neutral role. As one paper’s title runs, “Carbohydrate-restricted
diets high in either monounsaturated fat or protein are equally
effective at promoting fat loss and improving blood lipids.”8 The
primary difference is that in those who are overweight or obese,
as opposed to in individuals who are lean or normal weight,
fat has less satiating power than does protein.9 Otherwise,
as long as high-fat consumption is not a marker for generally
poor eating and exercise habits (low consumption of fruits and
vegetables, low consumption of fiber, high consumption of
sugars and refined carbohydrates), fat consumption, after 60
years of controversy, has not been shown to be innately a threat
to health.10 Just remember that the foods eaten at breakfast tend
to determine the body’s ability to retain metabolic flexibility
later in the day. Breakfasts that container significant fat do not
tend to interfere with the ability to metabolize fat rather than
store it later in the day, breakfasts built around carbohydrates
do, and protein is the great equalizer.
Conclusion
Whether it concerns mice or men, the timing of meals is
important. Eating more at breakfast and less at the evening
meal leads to better appetite control and better metabolic
functioning along with better weight control. Eating more
protein and fewer carbohydrates at the morning meal, likewise,
leads to greater metabolic flexibility later in the day. The
standard American breakfast of cold, sweetened cereal is a very
poor choice for control of appetite, energy levels or body weight.
Fats are a largely neutral in this picture, although they certainly
can replace a good portion of carbohydrates, especially if more
protein is consumed. The old adage to “breakfast like a king,
lunch like prince and sup like a pauper” turns out to be good
advice. Best of all, changing the timing and size of meals is
free!
References
- Hernandez-Morante JJ, Gomez-Santos C, Milagro F, Campión J, Martínez JA, Zamora S, Garaulet M. Expression of cortisol metabolism-related genes shows circadian rhythmic patterns in human adipose tissue. Int J Obes (Lond). 2009 Apr;33(4):473–80.
- Dallman MF, Akana SF, Bhatnagar S, Bell ME, Strack AM. Bottomed out: metabolic significance of the circadian trough in glucocorticoid concentrations. Int J Obes Relat Metab Disord. 2000 Jun;24 Suppl 2:S40–6.
- Bray MS, Tsai JY, Villegas-Montoya C, Boland BB, Blasier Z, Egbejimi O, Kueht M, Young ME. Time-of-day-dependent dietary fat consumption influences multiple cardiometabolic syndrome parameters in mice. Int J Obes (Lond). 2010 Nov;34(11):1589–98.
- Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, Leblanc M, Chaix A, Joens M, Fitzpatrick JA, Ellisman MH, Panda S. Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Cell Metab. 2012 Jun 6;15(6):848–60.
- Leidy HJ, Ortinau LC, Douglas SM, Hoertel HA. Beneficial effects of a higher-protein breakfast on the appetitive, hormonal, and neural signals controlling energy intake regulation in overweight/obese, “breakfast-skipping,” late-adolescent girls. Am J Clin Nutr. 2013 Apr;97(4):677–88.
- Jakubowicz D, Froy O, Wainstein J, Boaz M. Meal timing and composition influence ghrelin levels, appetite scores and weight loss maintenance in overweight and obese adults. Steroids. 2012 Mar 10;77(4):323–31.
- Jakubowicz D, Barnea M, Wainstein J, Froy O. High caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women. Obesity (Silver Spring). 2013 Dec;21(12):2504–12.
- Luscombe-Marsh ND, Noakes M, Wittert GA, Keogh JB, Foster P, Clifton PM. Carbohydrate-restricted diets high in either monounsaturated fat or protein are equally effective at promoting fat loss and improving blood lipids. Am J Clin Nutr. 2005 Apr;81(4):762–72.
- Brennan IM, Luscombe-Marsh ND, Seimon RV, Otto B, Horowitz M, Wishart JM, Feinle-Bisset C. Effects of fat, protein, and carbohydrate and protein load on appetite, plasma cholecystokinin, peptide YY, and ghrelin, and energy intake in lean and obese men. Am J Physiol Gastrointest Liver Physiol. 2012 Jul;303(1):G129–40.
- Schwingshack L, Hoffmann G. Comparison of effects of long-term low-fat vs high-fat diets on blood lipid levels in overweight or obese patients: a systematic review and metaanalysis. J Acad Nutr Diet. 2013 Dec;113(12):1640 – 61.