Wouldn’t our jobs as personal trainers be much easier if all there was to healthy weight maintenance and optimal well-being was striking a balance between calories in and calories out? It just is not that simple. If weight loss and metabolism were as simple as eating less and moving more, our jobs as health and exercise professionals may not be as valuable. Understanding the role blood sugar plays and how it is affected by macronutrient balance, and coupled with resistance training is vital to orchestrating optimal fat loss.

Now, this is not to say that a caloric deficit is not required for a shift in weight. It is. But too often weight loss is reduced to a simple “balancing” act. Here’s what the bigger picture entails and what health and exercise professionals need to remain cognizant of.

Blood Sugar is Queen

Blood sugar management and regulation do not always get the attention these processes require or deserve. Partly, because there is a misconception that only those with diabetes need to be concerned with what their blood sugar is doing. Not true. Blood sugar and its management are important biological and behavioral processes for all individuals – diabetic or not.

The Why

When blood sugar is on a constant daily rollercoaster, insulin is recruited more often (the “fat-storing” hormone). When insulin is at the forefront and working overtime, glucagon (or the “fat-burning” hormone) is on the bench. Instead, if you were to graph blood sugar response, it should resemble a gentle wave profile with subtle (and not drastic) rises and drops throughout the day.

The lesson for us all is this: a calorie deficit is important for weight reduction (and is only one component) but if your client is eating and operating in a calorie deficit, their hormones will not be as efficient at supporting fat loss (which is different than weight loss and a point that gets confusing for consumers). Ultimately, clients will have a harder time reaching their goals and are likely to experience frustration along the way. Let’s look at how blood sugar is impacted by both exercise and diet.

Hyperglycemia and Workout Capacity

We know that exercise is essential for good health, but high blood glucose, or blood sugar, levels can undermine or even cancel out the benefits of aerobic exercise.

Individuals with consistently high levels of blood sugar seem to derive less benefit from their workouts than their non-hyperglycemic counterparts, according to a cautionary new study of nutrition, blood sugar, and exercise. Consuming a diet high in processed foods could also alter how well our bodies respond to exercise.

Many clients open up to trainers during an initial assessment, not only regarding fitness goals but also other health and lifestyle struggles. Trainers have no doubt noticed throughout their careers that often clients who reveal issues with hyperglycemia tend to be deconditioned and overweight, placing them at a greater long-term risk for heart disease and Type 2 Diabetes, if these aren’t already factors. Epidemiological studies indicate that people with elevated blood sugar often also have a diminished aerobic capacity, closely linked to a high risk of premature death.

Blood Sugar Factor: Causation or Correlation?

Most studies linking blood sugar and fitness have identified correlations between the two; however, they fall short in clarifying how either condition influences the other. The answer to this key question has yet to be determined: Does hyperglycemia precede and lead to a reduced level of fitness, or does a lack of aerobic capacity foster high blood sugar levels?

The results of a recent study, documented and published in the journal Nature Metabolism, aim to shed light upon these very questions. Researchers at the Joslin Diabetes Center in Boston, in collaboration with other institutions, sought to explain how elevated blood sugar levels in mice affected their exercise capabilities, if at all.

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Vascular Remodeling

With regular aerobic exercise, the muscles of the control animals exhibited an abundance of healthy, new muscle fibers, along with increased blood vessels. Optimal vascularization such as this facilitates the shuttling of additional oxygen and fuel to the muscle tissues. In comparison, the same tissue in mice with elevated blood glucose levels displayed mostly new deposits of collagen, a rigid substance that crowds out new blood vessels, thereby preventing the muscles from “remodeling” and contributing to improved levels of fitness.

Finally, the scientists repeated this protocol with a test group of 24 young adults. During treadmill fitness testing, the subjects whose bodies displayed the worst blood-sugar control also exhibited diminished endurance. Upon microscopic examination of their muscle tissues following the exercise sessions, researchers noted the presence of proteins that actually inhibit improvements to aerobic fitness. The scientists propose that high levels of blood sugar may prevent muscle remodeling in part by modifying the “extracellular matrix” proteins in the region of blood vessel formation. This less-vascularized muscle tissue explains the observed lack of increase in aerobic fitness, in spite of diligent exercise.

Focus on Clients’ Overall Health

Sarah Lessard, an assistant professor at the Joslin Diabetes Center and Harvard Medical School and lead author of this study, advocates a combination of diet and exercise for optimal health. “The good news is that although our hyperglycemic mouse models did not improve aerobic fitness through exercise, they did achieve other important health benefits from exercise, including a reduction in body fat and improved glucose metabolism,” says Dr. Lessard. Therefore, regular aerobic exercise remains a key recommendation for maintaining health, regardless of blood glucose levels.

The adaptation of this muscle tissue points to the precise reason why the relative comfort of frequent and regular participation in exercise replaces that initial overwhelming exhaustion, Lessard says. With time, any vigorous aerobic exercise can alter muscle fibers towards greater oxygen utilization during aerobic workouts. “We also grow new blood vessels to allow more oxygen to be delivered to the muscle, which helps to increase our aerobic fitness levels,” she says. This points to chronic hyperglycemia as a potential negative regulator of aerobic adaptation. Such knowledge points to the importance of dietary/metabolic health in conjunction with exercise.

Blood Sugar and Meal Planning

First, always have a dietitian consult with clients who are pre-diabetic or diabetic. Both are conditions that require intervention. Second, keep in mind your certified scope of practice related to nutrition. Providing insight and information such as evidence-based recommendations, legitimate sources for recipes, leading grocery store tours, and meal-prepping skills and tools are all within your scope (among other things).

Three key suggestions and general guidelines you can recommend include encouraging clients to:

  1. Focus on a combination of protein, high fiber, and healthy fats at meals
  2. Pair carbohydrates with healthy fats and/or proteins (fruit with nuts or nut butters, whole-grain English muffin with eggs, etc.).
  3. Select the highest-fiber sources of starchy carbs (quinoa, whole grains, lentil pastas, oats, etc.).

Benefits Beyond Blood Sugar 

There are countless benefits associated with the guidelines above, aside from controlling blood sugar. Meals and snacks based on these principles offer greater satiety, higher mineral content, digestive system benefits, mental benefits, and energy. When clients are more satisfied with their meals, they are not preoccupied with thinking about food, tracking food, or obsessively measuring grams and ounces.

There is a food freedom that comes from balancing meals consistently instead of worrying about being over or under a certain caloric intake. The human body is not a calculator; it’s a complex set of systems that need the right fuel consistently (not necessarily the “right number”). Besides, there is no simple (or 100% accurate) way to measure a person’s caloric needs (aside from using a metabolic cart, and even then, there are errors in measurements).

Focus on protein, fiber, and quality fat sources and your clients will be able to better control their blood sugar and make their fat-burning hormones happy and optimally functional. We can share this with clients when discussing food choices, raising awareness about today’s soaring incidence of high blood sugar, both in adults and children. Addressing this topic early in the trainer/client assessment can foster trust as well as the evolution of more successful outcomes of their exercise-related goals.






Erin Nitschke

Dr. Erin Nitschke, NFPT-CPT, NSCA-CPT, ACE Health Coach, Fitness Nutrition Specialist, Therapeutic Exercise Specialist, and Pn1 is a health and human performance college professor, fitness blogger, mother, and passionate fitness professional. She has over 15 years of experience in the fitness industry and college instruction. Erin believes in the power of a holistic approach to healthy living. She loves encouraging her clients and students to develop body harmony by teaching focused skill development and lifestyle balance. Erin is also the Director of Educational Partnerships & Programs for the NFPT. Erin is an editorial author for ACE, IDEA, The Sheridan Press, and the Casper Star Tribune. Visit her personal blog at belivestaywell.com