Is Time Restricted Eating a Magic Bullet?
or just a simple way to restrict calories like any other
What is Time Restricted Eating
Time-restricted eating is a form of “Intermittent fasting” which could be called daily intermittent fasting. It is pretty simple, just stop eating for at least 12 hours…everyday, usually overnight (and then eat at other times of day).
What is the Point?
If you eat three times a day, you spend most of the day (and night) in an anabolic (ie fed) state; insulin is low but glucagon and growth hormone, are elevated. This signals your body to halt any fat burning, to store excess calories in your fat cells, and burn glucose (from your last meal) instead. Over time this leads to insulin resistance.
After the first few hours after a meal your body goes into a post–absorptive state, and then after 8 to 12 hours after your last meal a catabolic (or fasted state). This is shown in the shaded red area. If you eat only twice a day, or better once a day, then your hormonal state will adapt to this fasted state by returning insulin to normal.
By eating once per day your average insulin level is much lower, although it will spike following your meal, this is normal to control glucose.
Circadian Effects
Circadian rhythms are thought to be largely controlled by light and the brain but there are new discoveries of molecular clocks in individual organs. At the molecular level, the circadian clock is based on cell-autonomous feedback circuit driven by the basic helix–loop–helix-PER-ARNT-SIM (bHLH-PAS) transcription factors BMAL1 (no I have no idea what that means either 😂)
What is important is that the circadian clock is present in almost all tissues and cells. And there is a potentially important circadian rhythm in insulin release such that it is higher during the first half of the day. At night, the rise in melatonin before bedtime can inhibit glucose-induced insulin release from the pancreatic β cells. Hence, consuming a bigger portion of daily caloric intake in the first half of wakeful hours may be preferred for better blood glucose regulation, body weight control, and related health outcomes.
Further food resets the circadian rhythm. For example animals (? and some people!) will wake up a few hours before the arrival of food and start moving anticipating food. Such food-anticipatory activity would also occur when calories are reduced and presented at night and the magnitude of activity would increase with the reduction in calories.
When Should I Eat?
Actually, the exact hours don’t seem to matter, so you could do
12hr fast 12hr eating: normal IF method
16hr fast 8hr eating: Leangains method (by Martin Berkhan)
20hr fast 4hr eating: Warrior Diet method (by Ori Hofmekler)
In all these methods, you avoid eating later at night or early in the morning (usually skipping breakfast)….but wait….doesn't this breaks all those old-wives tales of eating:
“Breakfast is the most important meal of the day!”
“Eat small frequent meals.”
“Your metabolism slows down when you are fasting.”
“If I don’t eat I will get low blood sugar [hypoglycemia].”
Correct, but this is science. A huge new review has just examined all the animal and human data.
They examined 39 human studies ranging from 4 days to 1 year.
The most common finding was a decrease in body weigh and to a lesser extent improved glucose regulation (decreased fasting glucose and glucose area under the curve assessed via continuous glucose monitoring, improved insulin sensitivity, and increased β-cell function) was observed in 12 studies and additional benefits to cardiovascular health eg decreases in blood pressure.
No Magic Bullet
So all this evidence means it works right? True. But here comes the catch…..isn’t this just the same as calorie restriction by any method??
In other words, can you do intermittent fasting and not restrict your diet at all…and it still works? If so, then yes it would be like a magic bullet. One study has compared intermittent fasting with a normal timed but structured diet of similar calories and found no difference (see link) . What we need is one of two new types of study:
Intermittent fasting vs Normal Fasting (with the same calories)
Intermittent fasting vs usual diet (but with the same calories)
and in fact I found one such study……..in NEJM no less!
Liu et al. conducted an RCT of calorie restriction alone as compared with calorie restriction plus time-restricted eating in weight loss in 139 patients with obesity. All the patients were assigned a diet that represented a 25% calorie reduction from baseline to be followed for 12 months.
The trial tested whether 8-hour time-restricted eating plus calorie restriction was superior to calorie restriction alone.
The percent weight loss from baseline to 12 months was 9.0% (8.0 kg) in the time-restriction group but almost as good: 7.2% (6.3 kg) in the calorie-restriction-only group. Waist circumference, body-mass index, body fat, blood pressure, and biomarker levels decreased significantly over the trial time period with no differences.
These results of the trial suggest that time-restricted eating is roughly the same as calorie restriction however time-restricted all said, time-restricted eating seemed simpler, because caloric restriction needed intensive coaching and monitoring but time-restricted eating did not.
Calorie Controlled Animal Studies
Whilst we wait for more human studies, there are some hints from animal studies where calories were held constant but timing was varied. Irrespective of the time of day when the calorie restricted diet was given to mice consistently, in the morning, afternoon, or evening, calorie restricted led to an extended lifespan. In a short-term calorie restricted study, however, calorie restricted mice receiving food in the morning (during their circadian sleep time), experienced less weight loss than mice that received the same calories at night. These TRF rodents that consume the same calories as an ad libitum cohort from the same food source exhibit improved molecular rhythms in circadian clock components and are largely protected from high-fat diet-induced obesity and related metabolic illnesses.
Conclusion
Intermittent fasting is an effective way of reducing calories and gaining weight loss and additional health benefits.
It likely has new discovered benefits in terms of circadian rhythm.
However, it is *not yet* proven more effective than a rigorous calorie restriction diet by any other method
That said, if intermittent fasting works for you, then it is likely a good choice.
Citations
Time-restricted Eating for the Prevention and Management of Metabolic Diseases. Emily N C Manoogian, Lisa S Chow, Pam R Taub, Blandine Laferrère, Satchidananda Panda. Endocrine Reviews, Volume 43, Issue 2, April 2022, Pages 405–436,
