December 13, 2019
Eating a carbohydrate-rich breakfast followed by a substantial lunch and a small dinner — the so-called "three-meal diet" (3Mdiet) — promotes weight loss and significantly improves glucose control in type 2 diabetes, a randomized, controlled trial suggests.
In fact, the 3Mdiet improved glycemic control so significantly that patients could reduce their total daily insulin dose, along with the need for additional antidiabetic medications, relative to baseline, the same small study indicates.
"The traditional diabetic diet specifies six small meals spread throughout the day, but this '6Mdiet' as it is called has not been effective for glycemic control," lead author Daniela Jakubowicz, MD, professor of medicine, Tel Aviv University, Israel, explains in a statement from American Friends of Tel Aviv University.
"Our research proposes shifting the starch-rich calories to the early hours of the day [to] produce a glucose balance, and we believe that through this regimen it will be possible for diabetics to significantly reduce or even stop injections of insulin and most anti-diabetic medications to achieve excellent control of glucose levels," she added.
In the study, published in the December issue of Diabetes Care, the researchers hypothesize that the 3Mdiet is more in-sync with the natural biological clock — metabolism is optimized for eating in the morning and for fasting during the evening and night, when people are supposed to be asleep.
Both Diets Had Same Macronutrients and Calories
The trial involved 28 volunteers with type 2 diabetes of 5 years' duration or longer treated with insulin for at least 1 year prior to study entry, at a total daily insulin dose in excess of 25 units. The average body mass index (BMI) was 32.4 kg/m2 and average baseline A1c was 8.1%.
"Subjects were sedentary at baseline and were asked to maintain their usual physical activity levels," the investigators observe.
Patients were randomized to the 3Mdiet or 6Mdiet and followed for 12 weeks.
Importantly, "both diets had the same macronutrient composition of fat, protein, and carbohydrates (35%, 25%, 40%, respectively), but with different meal timing, frequency, and calorie and carbohydrate distribution over the day," the authors point out.
For example, participants on the 3Mdiet consumed a large breakfast of, for example, bread, fruits, and sweets, of around 700 calories, a medium-sized lunch of 600 calories, and a small dinner of 200 calories, specifically lacking starches, sweets, and fruits.
In contrast, those randomized to the 6Mdiet ate breakfast, lunch, and dinner along with three snacks of 150 calories each such that caloric consumption was relatively uniform across the day, with snacks scheduled for 11:00, 17:00, and 22:00 hours.
Significant Weight Loss With 3Mdiet
After 12 weeks of the intervention, those on the 3Mdiet lost on average 5.4 kg compared with a small 0.3-kg weight gain in the 6Mdiet group, a difference that was highly significant (P < .0001), the investigators report.
Over the same 12 weeks, participants in the 3Mdiet group had a 1.2% decrease in A1c compared with a nonsignificant decrease in the 6Mdiet group (P = .5).
The magnitude of reduction in A1c is comparable to the decrease seen with the addition of a glucagon-like peptide-1 (GLP-1) receptor agonist or a sodium-glucose cotransporter 2 (SGLT2) inhibitor in patients with type 2 diabetes treated with insulin, the investigators observe.
At the end of the study intervention, fasting glucose had dropped in both groups, but the reduction was more pronounced in the 3Mdiet group than in the 6Mdiet group.
Specifically, at week 12, fasting glucose had dropped to 110 mg/dL from 165 mg/dL at baseline in the 3Mdiet group, compared with 141 mg/dL from 164 mg/dL at baseline in the 6Mdiet group.
There was also a significant reduction in daily 24-hour mean glucose levels at 12 weeks in the 3Mdiet group compared with no significant change in the same glucose parameter in the 6Mdiet group (P < .05).
Continuous glucose monitoring (CGM) assessments in both groups also showed that time spent in normoglycemia increased from 59% at baseline to 83% at week 12 in the 3Mdiet group.
"In contrast, the 6Mdiet did not change the time spent in normoglycemia throughout the study," say Jakubowicz and colleagues.
Participants assigned to the 3Mdiet also experienced a significant decrease in hunger and overall cravings for sweets, fast food, and high-fat food by study end, whereas those assigned to the 6Mdiet did not experience any change in hunger or have less of a craving for the same foods.
And importantly, in spite of the significant improvements in glycemic measures observed in the 3Mdiet group, participants in that group were not at greater risk for hypoglycemic events.
Total Daily Insulin Dose Reduced With 3Mdiet
For those on the 3Mdiet, the total daily insulin dose dropped by 26 units across the study interval from 60 units at baseline to 34 units at 12 weeks.
Again, in contrast, there was a small increase of 4 units in the total daily insulin dose for those on the 6Mdiet across the same study interval.
The magnitude of reduction in insulin needs seen among those on the 3Mdiet is again comparable to that achieved with the addition of a GLP-1 agonist or SGLT2 inhibitor, the authors stress.
And they observe that the significant reduction in the need for insulin seen in the 3Mdiet group was also independent of any weight loss among the same participants.
This is in contrast to the usual pattern of insulin use and weight gain seen in type 2 diabetes, when many patients gradually require increasing doses of insulin to meet glucose targets.
This increase in the need for insulin often leads to a vicious cycle of weight gain, which in turn may increase insulin resistance, further escalating the need for insulin, continued weight gain, and the likelihood that patients will fall short of their glycemic targets.
The authors suggest that a circadian pattern of diet-induced thermogenesis in which thermogenesis peaks after participants consume a high-calorie breakfast might help explain why the 3Mdiet led to greater weight loss compared with the standard diabetic diet.