How to Eat: Fast and Break-Fast

By Jason Fung, MD

Several interesting recent studies regarding meal timing that deserve some attention. The first study, part of the Adventist Health Study 2, looked at a large cohort of relatively healthy people. Adults (>30 years old) attending Seventh-Day Adventist Church completed health questionnaires every 2 years. Over 50,000 people participated, and this particular study looked at meal timing and its relationship to body weight.

There is a very widely held opinion that eating more frequently will help reduce weight over time. However, there is virtually no data to support this assumption, and it has gained reputability only through mindless repetition. At first glance, it sounds pretty stupid.

You should eat constantly to lose weight? How does that work? That’s like saying you should spray your clothes with water more often so that it dries faster. Eating more often generally results in more overall food intake. And increased food intake is not highly likely to make you lose weight. Nevertheless, frequent repetition by authority figures can convince us of anything.

So this study looked closer look at this relationship. Not surprisingly, the more frequently you ate, the heavier you are likely to be. Doesn’t really seem like rocket science. If you constantly eat meals and snacks, you will gain more weight. No sh**, Sherlock. The advice to eat constantly to lose weight sounds really stupid, because it is really stupid.

The study also noted that the longer you fast (18-24 hours) the more less you weigh. Again, not really hard to understand. If you give your body a good amount of time to digest your food and burn stored food (body fat) then you will likely weight less. This jives perfectly with much of the data on intermittent fasting and restricted eating windows.

But there is more interesting data here. Eating breakfast is considered a very important part of weight loss. Are they correct? Indeed, yes.

If you eat breakfast, you are more likely to weigh less. At first glance, it seems hard to reconcile the data. You want to eat less, have a long nightly fasting period, but still eat breakfast? How does that work?

Well, the answer lies in the circadian rhythm, which I’ve written about previously. Recall that insulin, not total calories is the main driver of obesity, although there is an overlap, to be sure. Different foods elicit different insulin responses, and therefore have different propensities to cause obesity. That is, 100 calories of cookies are more fattening than 100 calories of broccoli, despite what all the mindless calorie zombies tell you.

The same food will also elicit different insulin responses at different times of the day. Eating the same food at dinner (compared to breakfast) gives you almost 30% more insulin effect. In other words, food is more fattening when you eat it later at night. But the bad news for late eaters does not stop there. If you look at the circadian rhythm for hunger, you’ll find that hunger is lowest in the morning and greatest in the evening 8:00 pm or so.

Another study (Bo, S et al) found the same phenomenon. In this crossover study, they took 20 healthy people, gave them the same meal but either in the morning or evening. So both arms had exactly the same people, eating the exact same meal, but only differing by time of day. The evening meal stimulated significantly higher blood glucose and blood insulin response and insulin is the main driver of obesity. Even more interesting, the evening meal produced a much lower resting energy expenditure afterwards compared to the morning meal.

So, if you eat your largest meal in the evening, you suffer from 3 problems. You’ll be more likely to eat more (because you are more hungry – yikes), you’ll get more fattening effect for the food that you do eat (higher insulin – double yikes), and you’ll have lower energy expenditure (more calories will get turned to fat). TRIPLE YIKES!

So, to be clear. If you eat one meal a day, best make it breakfast. If you eat two meals a day, best make it breakfast and lunch. BUT eating 3 meals (breakfast/lunch/dinner) is not necessarily better than 2 (lunch/ dinner), which is often the message given out by the ‘Never skip breakfast’ mafioso. The best solution is to eat a large breakfast/ lunch and eat very little or no dinner. This gives you the benefits of both fewer meals and longer night time fast.

So why do I skip breakfast myself?

Because that schedule of eating does not fit my lifestyle. I tend to eat dinner with my family every night, and we rarely eat breakfast together as a family, because we’re rushing to school and work. So I skip breakfast, because it fits my lifestyle, and eat dinner. This is not optimal, but it is what works for me. I still get the fewer meals, and the longer night time fast, but I get the disadvantage of high insulin effect at night. However, it is precisely this knowledge of science and practical experience that allows us at the Intensive Dietary Management program to devise individualized schedules for people. Trying to shoehorn an eating schedule into an incompatible life schedule is weight loss suicide.

The other recent study that was fascinating was the MATADOR study. In this randomized study, patients either received energy restriction either as a constant 8 week block, or in 2 week chunks alternating with 2 week blocks of no energy restriction (eventually totalling 8 weeks of energy restriction).

So both groups got identical calorie restriction and standardized diets, but one of them (Control) got 8 weeks straight of ‘dieting’ then 8 weeks of ‘no diet’. The other group (Intermittent) got 2 weeks of ‘dieting’ followed by 2 weeks of ‘non dieting’ for a total of 8 diet weeks.

Does the ‘intermittency’ of the diet make a difference? You bet the hell it did. Not only was far greater weight loss after 16 weeks, but at 6 months, the difference in weight was 8.1kg – 17.8 pounds! Jay-sus. There was weight regain in both groups at 1 year, but things looked a lot better in the intermittent diet.

What explains this huge difference? The answer is the change in resting energy expenditure (REE) also known as basal metabolic rate. The REE is how much energy is burnt by the body at rest (not at exercise). This is the energy (calories) used up in generating body heat, keeping the brain, lungs, liver, kidney, heart etc. working properly. This is not a static number but changes up to 30-40% depending upon the hormones. As you lose weight, the REE goes down (less body mass to heat, less energy needed) so you need to adjust the REE for Fat Free Mass (FFM) and Fat Mass (FM). Decreased REE is the main reason for the failure of The Biggest Loser contestants.

Constant energy restriction steadily decreases REE. This is why the constant calorie restriction as the primary method of weight loss is a consistent loser. If you cut, say 500 calories from your diet every day, as many health authorities recommend, your body will simply adjust by burning less. This Caloric Restriction as Primary (CRaP) method is doomed to fail. As you eat less, you burn less. Eventually you plateau and then you start the weight regain. Tears follow the silent accusations of your doctor that you just didn’t have enough will power. But the fault was not your. It was physiology. It happens to everybody.

Instead, if you ‘diet’ intermittently, the body does not adjust and REE stays significantly higher. You have more energy, you don’t feel so cold, and weight stays off. It is the INTERMITTENCY of the diet that makes it successful. We talk constantly about the question of ‘What to Eat’ but almost never consider the equally important question of ‘When to Eat’. That is the reason, in my Intensive Dietary Management Program, we stress that you sometimes need to change things up.

One common question is whether eating one meal a day is acceptable. That is a daily 23 hour fast. Sounds pretty good. And it works well for a lot of people. But a lot of people will also plateau at a weight higher than they would like. At that point, we suggest that they do something to change the schedule. Sometimes we’ll suggest changing the diet, and other times we’ll suggest changing the fasting regimen. If you have plateaued, just do something different.

Lastly, I’d like to say a few derogatory words about the recent study about skipping breakfast and getting heart disease   – based on 4000 adults in Spain, breakfast skipping was associated with more heart disease. The media is having a field day proclaiming that skipping breakfast causes heart disease. Oh, My, God. You must always eat breakfast, even if it is a Krispy Kreme donut! Oh, My, God. I can’t believe you have been awake for almost 2 minutes and haven’t started cramming food into your mouth. Call 911! Oh, My, God. You need to sleep in the kitchen so you can shovel food into your mouth before your feet hit the floor. By the way – why can’t you lose weight?

Even the author is not so stupid as to suggest a causal relationship. He said ‘It’s not that you skip breakfast, you get plaques’. Of course not. People who skipped breakfast were also at higher risk of heart disease for other reasons, too. It’s kind of like saying that people with grey hair are at higher risk of dying (true – because they tend to be older). Therefore, to reduce the risk of dying, you simply need to dye your grey hair black. There’s a clear association with having an ‘A’ on top of your test and doing well in school. So, obviously, to do well in school, you should write ‘A’ on top of every test your write so you’ll do well. It’s absurd. But that doesn’t stop the media hype.

Understanding the science helps cut through the bull. There’s nothing wrong with eating breakfast. Eating more at breakfast and less at dinner makes physiologic sense for weight loss, because it reduces the insulin effect. But if you eat the same dinner but add breakfast, don’t expect that eating more food makes you lose weight.

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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