Metabolism is defined as the chemical changes that take place in a cell or an organism. These changes make energy, and the materials cells and organisms need to grow, reproduce, and stay healthy.

Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand. This is important to explain insulin resistance and metabolic syndrome as well as weight. If you can flex your body’s fuel selection between sugar/glycogen or fats/ketone you may not only lose weight but overcome the, metabolic inflexibility of obesity and type 2 diabetes.¹When you can metabolize fat or carbohydrates, you can burn calories and lose or maintain weight.

What governs metabolic flexibility?

Exercise has a profound effect on metabolism. You burn the most fat when you are between 45-65% of VO2 max.² You can count your VO2 max. The most common way to calculate your maximum heart rate is to subtract your age from 220.  Multiply that number by 0.45 and 0.65 and that is the range of heart rate where you will burn the most fat. Exercise intensities that exceed the crossover point (~65% VO2max) utilize carbohydrate as the predominant fuel source for energy supply.² So if you want to burn fat, stay within the 45-65% of target heart rate.

• Stay active and move.
• To lose fat, work at 45-65% of your target heart rate.
• Eat carbohydrates and protein within two hours after your workout.

Sleep disturbances are linked to circadian rhythm disturbances which are linked to being overweight. In a study measuring wrist temperature which is a marker for circadian rhythm, it was found that sleep quality was the only variable significantly related with both being overweight and circadian pattern. Social jet lag, the discrepancy of sleep time on weekdays versus weekends was not associated with weight gain and circadian rhythm disturbances.³ However social jet lag is associated with unhealthy behaviors and eating more high calorie, high sugar food, ^4,5 and is linked to diabetes, low HDL (the good cholesterol), high triglycerides, and its effect on weight was mixed. ⁵ Not getting enough sleep increases the loss of muscle mass and makes it hard to stick to a diet. ⁶

• Get 7-9 hours of sleep every night.
• Stop eating 3 hours before bed. It helps the body shift to morning fat burn.
• Stick to the same sleep schedule and wake up and go to bed the same time.

Meal timing is an important strategy for metabolic flexibility and weight loss. Diets can increase hunger and cravings and increase the production of ghrelin, a hormone that makes you feel hungry. A high protein and carbohydrate breakfast may overcome these changes and prevent relapse and regaining weight that you lost.⁷ Eating the main after 3 PM, was predictive of difficulty in weight loss.⁸

There are circadian clocks in stomach, intestine, pancreas, and liver related to food intake. Daily food patterns govern fat gain or fat loss. ⁸ Eating late at night and shift work or out of sync with the circadian rhythm, is associated with increased risk for diabetes and insulin resistance. The appropriate rhythm depends on a persons chronotype (morning person or night owl) and melatonin production. Eating late when light is low and melatonin production is high, does not allow blood sugar to clear.

Study subjects who ate a high caloric breakfast (700 kcal) and low caloric dinners (300 kcal) lost significantly more weight than those who had low caloric breakfasts and high caloric dinners. Evening chronotypes who eat two hours before sleep had a 5 times increased probability of being obese. Morning chronotypes with high caloric intake two hours after wake time have a 50% decreased probability of being obese.⁹

• Eat your calories early.
• Make your lightest meal at night.
• Do not eat later than 2 hours before bedtime (preferably 3).

A personalized plan to lose and maintain weight is important to develop and stick to. If you need assistance, fill out a free diet evaluation. Let us help you look and feel good again.

1. Goodpaster BH, Sparks LM. Metabolic Flexibility in Health and Disease. Cell Metab. 2017;25(5):1027-1036. doi:10.1016/j.cmet.2017.04.015
2. Purdom T, Kravitz L, Dokladny K, Mermier C. Understanding the factors that effect maximal fat oxidation. J Int Soc Sports Nutr. 2018;15:3. doi:10.1186/s12970-018-0207-1
3. Zerón-Rugerio MF, Diez-Noguera A, Izquierdo-Pulido M, Cambras T. Adiposity and body mass index of young women are associated with altered 24-hour profile of wrist temperature and sleep quality. Chronobiol Int. 2020;37(11):1580-1590. doi:10.1080/07420528.2020.1785486
4. Almoosawi S, Palla L, Walshe I, Vingeliene S, Ellis JG. Long Sleep Duration and Social Jetlag Are Associated Inversely with a Healthy Dietary Pattern in Adults: Results from the UK National Diet and Nutrition Survey Rolling Programme Y1⁻4. Nutrients. 2018;10(9):1131. doi:10.3390/nu10091131
5. Caliandro R, Streng AA, van Kerkhof LWM, van der Horst GTJ, Chaves I. Social Jetlag and Related Risks for Human Health: A Timely Review. Nutrients. 2021;13(12):4543. doi:10.3390/nu13124543
6. Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010;153(7):435-441. doi:10.7326/0003-4819-153-7-201010050-00006
7. Jakubowicz D, Froy O, Wainstein J, Boaz M. Meal timing and composition influence ghrelin levels, appetite scores and weight loss maintenance in overweight and obese adults. Steroids. 2012;77(4):323-331. doi:10.1016/j.steroids.2011.12.006
8. Garaulet M, Gómez-Abellán P. Timing of food intake and obesity: a novel association. Physiol Behav. 2014;134:44-50. doi:10.1016/j.physbeh.2014.01.001
9. Lopez-Minguez J, Gómez-Abellán P, Garaulet M. Timing of Breakfast, Lunch, and Dinner. Effects on Obesity and Metabolic Risk. Nutrients. 2019;11(11):2624. doi:10.3390/nu11112624

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