It sounds like clickbait, doesn't it? But there’s a powerful psychological hack with a big potential payoff that I share with my patients. It has to do with when you brush your teeth.
Get the timing right, and you could significantly boost your health in terms of improved energy levels, sleep quality, lower blood sugar levels, and weight control.
Table of Contents
The Intermittent Fasting Controversy
To show you why, I need to explain the intermittent fasting controversy and the mistakes we’ve now corrected. And yes, this does all link back to the timing of when you brush your teeth.
The initial excitement about intermittent fasting came from studies on rodents, where calorie intake was restricted to a small window each day. They found this feeding strategy reduced weight, improved blood sugar control, lowered insulin levels, and increased lifespan [1]. And here’s the critical point: even when food intake is matched to the control group [1].
Here’s why that last point is so important. We already knew from previous rodent studies that restricting calories extends rodent lifespan. And we might expect that having a shorter window in which to eat leads to eating fewer calories. If true, that could explain the benefits seen.
But in these time-restricted feeding studies, both groups of rodents ate the same amount of food. So it wasn’t the amount of food that was driving the benefits seen, but the fact that rodents were eating this food within a shorter window of time.
This finding led to an explosion in popularity of time-restricted feeding. People usually call it intermittent fasting. Even for those who don’t need to lose weight, it was hoped that if humans also ate within a small timeframe each day, we, too, could live longer and be healthier [2], [3].
So does this eating strategy offer the same benefits for humans as for rodents? Well, first we need to understand what’s going on. Why was time-restricted eating having this impact in rodent studies?
When rodents were in the fasting period each day, scientists took biopsies. They saw that a process called autophagy was occurring in the cells of these mice. Autophagy is the cell clearance process, where old and damaged components are flushed away so new components can be built [4].
The evidence suggests autophagy can play an important role in extending lifespan.
That sounds really exciting, but we’re not rodents. So what do human clinical trials show?
We currently lack evidence that time-restricted eating triggers autophagy in humans the same way it does in rodents. This may be because the metabolic system of rodents differs so much from ours. You’ve probably heard of “dog years,” the idea that dogs age 7 years for every 1 human year. Something similar is true for rodents. One rat day equals around 27 human days [5].
That means we might need to fast for several days to see the same effects rats experience by fasting just a few hours.
Especially when you consider that our liver stores energy in the form of glycogen, and it can take up to 48 hours to burn through our glycogen stores before autophagy can be meaningfully activated [6].
But what about time-restricted feeding’s effects on weight and blood sugar levels?
At first, the research looked promising. A 2020 meta-analysis of human studies suggested that time-restricted feeding offered greater weight loss and reductions in blood sugar levels than other diets where people could eat whenever they wanted [7].
That sounds like the results match the rodent studies. But if we dig deeper, we find a big problem. Most of the studies that looked at time-restricted feeding had a fatal flaw. The time-restricted feeding groups ate fewer calories than the control groups [7].
To know whether time-restricted eating actually helps, we need to compare groups eating the same amount of calories. That’s precisely what the Cochrane organization did in 2021 through a careful meta-analysis. They found that in the trials that matched calorie intake between both groups, there were no differences in weight loss or blood sugar levels [8].
So, the take-home message here is: any benefits from time-restricted feeding are because we’re eating fewer calories. There’s no extra magic happening.
Timing
But there is something really important about meal timing. And the evidence shows most of us are getting this wrong, and it relates back to when we brush our teeth.
Our bodies have a natural rhythm, called the circadian rhythm. We go through a sleep-wake cycle over a period of 24 hours. It isn’t just about whether we’re awake or not, though. Many other bodily functions follow a daily cycle. And this includes digestion.
So when we eat impacts how our bodies handle food. For many of us in the West, our eating follows this pattern: a light breakfast, medium lunch, and heavy dinner. And we’re often eating that dinner relatively late. Even those following a time-restricted eating pattern often do something similar. They skip breakfast and pack most of their calories into the later part of the day. But this isn’t the best approach.
Part of the reason why is connected to weight. Maintaining a healthy BMI is a crucial factor in overall health. One analysis of over 500,000 adults with a follow-up of up to 20 years found this striking connection. The risk for all-cause mortality was 21-108% higher for those with a BMI of 30 and above [9].
This is because excess weight connects to many other important factors, from cholesterol levels, to blood pressure, to inflammation. And with an epidemic of obesity, this is an area we need to get right.
So how does meal timing connect to weight? One of the first studies to look at this question directly involved mice. Researchers fed two groups of mice the same high-fat diet. But one group ate during the normal time for mice. The other ate during a time that wouldn’t be typical. The mice that ate at the normal time gained less weight [10].
Does this pattern hold for humans, too? A more recent study divided those pursuing weight loss into those who ate lunch early and those who ate lunch late. The late eaters lost less weight during treatment [10].
But this was just an observational study. Researchers were interested in what mechanisms might be driving the difference. So the same researchers designed a randomized trial with standardized meals. They divided participants into those who ate lunch at 1 pm and those who ate at 4:30 pm. This revealed some really interesting findings. The late eaters burned less energy. They used carbohydrates less efficiently. Their bodies didn’t process glucose as well. And the later meal disrupted their cortisol patterns [11].
And this showed that when we eat is connected to crucial factors — like blood sugar control — that link to weight and other health problems like type 2 diabetes. A separate study looked at blood sugar response after breakfast in comparison to dinner. Participants ate the same meal at both times. The results were similar to the study with lunch. The meal eaten late in the day elevated blood sugar a lot more than when it was eaten in the morning [12].
And it isn’t just a matter of blood sugar control. Additional research found a morning meal stimulates our body to burn more calories compared to the same meal eaten in the evening [13].
Together, these results point to two important principles. Timing matters. Earlier is better because of how our bodies respond. Secondly, the distribution of calories matters. Intuitively, since we process food better in the morning, having more of our calories earlier should help if we want to manage weight.
Does research back this second principle up? Well, one study randomized participants into two groups. One ate the typical Western pattern: light breakfast, larger lunch, and the biggest meal at dinner. The other group did the opposite. But the total of calories eaten was identical [14].
What happened? The bigger breakfast group lost more weight. They also saw bigger improvements in blood sugar control [14].
The data we’ve looked at so far would lead us to expect these outcomes. But two other findings are surprising. First, the big breakfast group had a whopping 33.6% decrease in triglycerides. Triglycerides are a common form of fat that is found in the blood. Elevated triglycerides are a risk factor for heart disease and are associated with metabolic syndrome. So a drop like this is a big deal. In contrast, the big dinner group had their triglyceride levels rise by almost 15% [14].
The other surprise was that the big breakfast group also experienced less hunger throughout the day [14].
This is just one small study. A recent meta-analysis also found that eating more of our calories earlier helped with weight loss. The authors cautioned, however, that there are some issues with study quality. This is an area where we need ongoing investigation [17].
But from the evidence we have so far, including a strong connection between later eating and higher BMI, it looks like our best strategy is to reverse the normal Western eating pattern. I like to tell my patients to breakfast like a king, lunch like a prince, and eat dinner like a pauper. And shoot for an early dinner.
But what’s early when it comes to dinner? Experts usually recommend having our last meal at least 3 hours before bed. That gives us time to digest our food so our bodies can shift into night mode. If we have an early, light dinner and stop eating, our body focuses on repair instead of digestion, which helps improve sleep quality.
We’ve all probably experienced this: We eat a late, heavy meal and have trouble sleeping. A population-based observational study shows this problem is common. It looked at people’s sleep quality when they ate less than an hour before bed. Women were twice as likely and men 2.5 times as likely to be awake more than 30 minutes during the night when they ate like this [15].
A clinical study had similar results. It found that eating closer to sleep had a negative impact on several measures of sleep quality [16].
So eating earlier means we sleep better. Sleep is a crucial time during which our bodies are repaired and restored. Sleeping better means more energy — both physical and mental — the next day.
The Hack
And now it’s time to explain the hack.
We’ve seen our best strategy is to concentrate calories early in the day and then have our last meal a long way before bed. This is tough to do. Many of us are in the habit of reaching for a snack close to bedtime.
The solution is to start a new habit. Half an hour after I eat dinner, I brush my teeth. It gives my mind a clear boundary: my teeth are clean — I’m done eating for the day.
It’s super simple, but it’s effective. After a couple weeks, this becomes a habit we don’t have to think about. And we automatically fall into a pattern of eating that’s a lot better for our long-term health.
References
Below are all the study links in the order they appear:
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6627766/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990190/
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC5355425/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5355425/ (same paper discussing rodent-human time translation)
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8151159/
7. https://iris.unito.it/retrieve/handle/2318/1739566/635675/Bo%20et%20al%20Revised.pdf
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC10321632/
10. https://pmc.ncbi.nlm.nih.gov/articles/PMC6893547/
11. https://pubmed.ncbi.nlm.nih.gov/25311083/
12. https://pmc.ncbi.nlm.nih.gov/articles/PMC6266071/
13. https://www.nature.com/articles/ijo2015138
14. https://onlinelibrary.wiley.com/doi/10.1002/oby.20460
15. https://pubmed.ncbi.nlm.nih.gov/34511160/
16. https://pmc.ncbi.nlm.nih.gov/articles/PMC3227713/
17. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2825747
Note: All direct quotations from the studies have been removed, per your request. The rest of the script remains intact, including word count and language, with only minimal changes to fit a written blog format.
