When to Eat and Not Eat, How Many Meals and Intermittent Fasting

The whole matter of ‘when we eat’ meals and ‘when we don’t eat’ was historically a non-issue; we ate when it was daylight and we had food available, and we didn’t eat when it was dark or had no food. With the creation of indoor lighting and electricity, “day” lasted as long as we keep the lights on and for most of us, food is available in our fridges around the clock. Before elaborating on the current science surrounding when to eat meals and to not eat, let’s look at a short history of the origins of eating 3 meals per day, and when the idea of ‘snacks’ became prominent.

Timing of Meals

According to food historian Ivan Day[1], during the Middle Ages, availability of daylight shaped meal times, as there was no electricity. People got up and began to work in the fields at first daylight and by mid-day they were hungry after working for 6 hours or so and lunch was the first and main meal of the day. As there was no artificial lighting, cooking large meals in the evening simply wasn’t possible, so dinner was really a smaller meal, such as bread and cheese.

Breakfast became popular during the mid-19th century when labourers needed an early meal to sustain them at work. It became widely popularized in the early 20th century when John Harvey Kellogg invented the first breakfast cereal. Dinner became the main meal of the day with the creation of artificial (gas) lighting, and by the early 1900s, people were eating 3 meals per day, with the last meal occurring after work. Gas lighting was expensive to run, so after dinner was eaten and cleaned up from, bedtime was shortly after.


“Snacks” were frowned upon by the middle class during Victorian era because they did not require use of “proper” utensils (cutlery, plates), were seen as unhygienic and were associated with the lower class [2].

Snacks as we know them took root in the 1950s due to the manufacturing industry’s drive to sell new products in a growing economy after the end of WWII, along with an ability to create inexpensive disposable packaging and unique labelling to market these products. Sale of snack foods escalated in the late 1970s [2], and between 1977 and 2006, Americans were eating approximately 570 calories more per day, much of it as snacks rather than during meals [3].

Historic Dietary Treatment of Diabetes

Before the discovery of insulin, successful management of diabetes involved restricting carbohydrates eaten at meals.

In his text book titled “The Principles and Practice of Medicine” (1892), Dr. William Osler recommended a diet of 65% fat, 32% protein, and 3% carbohydrate, as well as abstaining from “all fruits and garden stuff.” [4] — not dissimilar to some of the high-fat “keto” diets available today. 

In the early 1900s, Bernard Naunyn encouraged a strict carbohydrate-free diet [5], with energy being provided as fat and protein.

In 1914, Dr. Frederick M. Allen treated people for several days with a period of fasting to clear the excess blood sugar via the urine, and then followed that with a diet that was mostly fat and protein, with a small amount of carbohydrates, mostly as vegetables ⁠[6].

Dr. Elliot P. Joslin was the first doctor in the United States to specialize in treating diabetes, and in 1916 adopted the same low-carbohydrate approach as Fredrick Allen [7].

Medications as Treatment in Diabetes

Type 1 Diabetes

The discovery of insulin by Dr. Fredrick Banting and Dr. Charles Best in 1921 provided life-saving therapy for those with type 1 diabetes (which results from failure of the insulin-producing  β-cells of the pancreas). The insulin was initially isolated from the pancreases of beef and pigs, but “human insulin” became possible in the 1980s due to recombinant DNA technology which enabled the development of both basal insulin, as well as rapid acting insulin. This was life-changing and life-saving to those with type 1 diabetes.

Type 2 Diabetes

Metformin initially became available as a first-line treatment for type 2 diabetes in the late 1990s, and enabled those with type 2 to better control their blood sugar levels along with dietary changes — but when people were unable, or unwilling to adequately limit carbohydrate intake, insulin was prescribed.

Insulin went from being a life-saving therapy for those with type 1 diabetes to  also being a ‘treatment’ for people with type 2 diabetes who ate what they wanted at meals and snacks and “covered it with insulin“. The problem is that this type of “liberalization” of the diet creates a “vicious cycle” for those with type 2 diabetes, described as follows in a new study published ahead of print in September 2019, and to appear in the December 2019 journal, Diabetes Care[8];

“Dietary intervention is usually accompanied by sequential addition of several anti-hyperglycemic agents, including glucagon-like peptide 1 (GLP-1) analogs and sodium–glucose cotransporter 2 (SGLT2) inhibitors. Despite this medical treatment, many patients require insulin therapy, which is gradually augmented according to the glucose target-driven strategy. However, this progressive increase in insulin dose often leads to weight gain, which may increase insulin resistance, leading to a vicious cycle further increasing insulin doses, continued weight gain, decreased likelihood of achieving glycemic targets, a high risk for diabetes complications and increased insulin dose-dependent cardiovascular risk and mortality. It is, therefore, important to prevent the weight gain when insulin treatment is required.”

Of course, medications such as biguanides, sulfonylureas, SLP-1 analogues and SGLT2 inhibitors are very important tools for doctors to add in helping manage blood sugar levels, but too often they are used instead of / in the absence of carbohydrate reducing dietary changes and this results diabetes becomes “a chronic, progressive disease“. It need not be so if people are willing to reduce their carbohydrate intake and time when they do eat some carbohydrate-containing food, in accordance with when their body handles them best.

Dietary Recommendations – meals and snacks

Since 2009, people with type 2 diabetes have been advised to eat 3 meals per day plus several snacks per day ⁠— with carbohydrates evenly distributed across the meals and snacks, in order to achieve the best weight management and blood sugar control [9-11].  They’ve been told to aim for between 45-60 grams of carbohydrate at each meal, and 15-20 grams of carbohydrate for each of 3 daily snacks (between breakfast and lunch, between lunch and dinner, and before bed). Surprisingly, the new study referred to above that will appear in the December 2019 issue of Diabetes Care states that there were no research studies to support these practices [8].

The 45-60 g of carbs for each of 3 meals per day and 15-20 g per snack distribution is still being recommended as goals to those with type 2 diabetes — resulting in between 190 -240 g of carbohydrate being eaten each day. That is a lot of carbohydrate for people who’s bodies can no longer handle that much. Presumably the snacks are to lower the risk of hypoglycemia (low blood sugar) that can result from the anti-hyperglycemic medications that have become necessary to prescribe because these people do not restrict carbohydrate and as a result have blood sugar levels that are too high.

Most concerning is that recent studies have found that snacks consumed later in the day have been associated with an increased risk of obesity and type 2 diabetes, with higher overall blood sugar and higher glycated hemoglobin (HbA1C) [12-13]. These are some of the “costs” of people being told to eat an afternoon and evening snack in order to avoid low blood sugar that can result from taking medication to lower blood glucose, and in an absence of being willing to reduce carbohydrate intake.

Would it not make far more sense to encourage people with type 2 diabetes to eat less carbs and eat less often — along with doctors de-prescribing anti-hyperglycemic medication, including insulin? That way, no snacks are needed to keep them from having low blood sugar and their average blood sugar levels can fall.

In fact, a soon-to-be-published pilot study [8] found that those with type 2 diabetes who ate the same calories each day as 3-meals per day, rather than as 6 meals per day [i.e. 3 meals and 3 snacks] reduced body weight, blood glucose, and insulin dosesWithout even changing how many carbs they ate or how many calories they ate, in just 12 weeks, the subjects in the 3 meal per day group, lost on average 12 pounds (5.4 kg) more than those in the 6 meal per day group, had 1.2% lower HbA1C than the 6 meal per day group and their total daily insulin dose was reduced by 26 units ± 7 (with no reduction in the 6 meal per day group). On top of this, this study found that “there was a significant decrease in hunger and cravings only in the 3 meal per day group“. This makes sense of course, because they were able to lower their injected insulin, which drives hunger and fat storage, leading to weight gain. The mechanism was thought to be an up-regulation in the clock genes of those that ate 3 meals per day, which contributed to the improved glucose metabolism.

Note: it’s important to keep in mind that it is the eating of carbohydrate-containing food that triggers the release of insulin from our pancreas, so even in healthy people i.e. those who are not diabetic, eating the same amount of food as 3 meals per day with no snacks (versus 3 meals plus 3 snacks) will result in less insulin being released. Less insulin means less hunger and less fat storage — whether it is the natural insulin from our own pancreas or it is injected insulin. If our goal is weight management, eating the same amount of food as 3 meals, rather than as meals and snacks makes sense.

This study verified that when we eat and when we don’t eat matters a great deal because our body has evolved over hundreds of thousands of years to function in response to light and day cycles, called circadian rhythms.

When We Eat – especially which meals to eat carbs

Chronobiology is the study of the effect of time of day on living systems and is emerging as an important player in human health.

We now know that the body’s processes involved in the maintaining of blood sugar control such as β-cell function, glucose uptake by the muscles, and glucose production by the liver, are all under the control of circadian rhythms. The body’s “master clock” which controls these circadian rhythms is found in a part of the hypothalamus of our brain, called the suprachiasmatic nucleus (SCN) and is “set” by exposure to light.

Note: Historically, the only light that set the SCN was sunlight, but our increasing exposure to bright lights emanating from office- and store- lights, TVs, computers and smart phones has disrupted this once tightly regulated system. 

Similar “peripheral clocks” are found in our body’s tissues, including muscle cells, liver cells, β-cells of our pancreas which produce and release insulin, and fat cells (adipose), and these are controlled by the “master clock” in our SCN, and by when we eat [14,15]. 

As it turns out, our circadian rhythms are optimized for us to eat during periods of light (daytime), and to fast and sleep in periods of dark (night time) [16,17] — so fasting after supper and overnight is consistent with our body’s built-in circadian rhythms.

In addition, blood sugar control is not the same at all times of the day, but fluctuates according to our body’s circadian rhythms. It has been shown in both healthy individuals and those with type 2 diabetes that identical foods eaten in the afternoon and evening cause much higher elevations in blood sugar, compared with the same foods eaten in the morning [18-20] . Based on this, it makes the most sense for any major carbohydrate sources (milk, fruit, root vegetables etc.) that are going to be eaten during the day to be consumed at breakfast, rather than evenly distributed across the whole day and evening.

When We Don’t Eat – intermittent fasting

It has been shown for those with type 2 diabetes that fasting until noon time actually results in much higher after-meal blood sugar levels (postprandial hyperglycemia), as well as an impaired insulin response after lunch and dinner [21], so while it is currently popular for people to chose their “eating windows” based on a wide range of popular protocols, it seems to me that choosing them in a way that is consistent with our circadian rhythms makes the most sense — especially if the goal is weight loss, appetite control and blood sugar regulation.

More Info

If you would like more information about having me design a Meal Plan for you that arranges your eating times and non-eating times around your schedule and in accordance with your natural circadian rhythms, please have a look under the Services tab or in the Shop. If you have service-related questions, please feel free to send me a note using the Contact Me form above, and I will reply as soon as I can.

To your good health!


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