No matter how strict your diet or how consistent your training, certain stressors make it difficult for you to lose fat. One of these is out-of-range blood sugar.
Using a glucometer to monitor your fasting blood sugar each morning will let you know if you're making energy through gluconeogenesis.
Cortisol is released in a diurnal (24-hour) rhythm. It's higher after waking, and then decreases throughout the day to an evening low. This rise in morning cortisol is called the cortisol awakening response (CAR). The purpose is to stimulate glucose production to ensure there's sufficient energy to start the day. However, there are many reasons for variations to this rhythm, which can be identified with testing.
Identify the Problem
If you're struggling to lose fat, monitoring fasting and post-prandial (after eating) glucose might help to identify the problem. The ideal range for fasting and 2-hours post-prandial glucose is 74-88 mg/dL (4.1-4.9 mmol/L).
While it's beyond our scope here to discuss all the mechanisms for post-prandial elevation, the important point is that levels outside these ranges will affect your ability to lose fat. If these are elevated, it's important to investigate. Begin by taking a close look your diet, exercise, and other stressors such as sleep.
When fasting blood sugar isn't in range, it's unlikely to be due to excessive carbohydrates or extremely poor insulin control (overfed cells, insulin resistance, or poor first phase insulin response). The reason, which can be confirmed with blood tests, (called OAT and DUTCH testing) may point to what's most likely some form of cortisol dysregulation.
The cortisol awakening response is normal in the morning to get us up and going, and it does this partly by raising our blood sugars. But when these are raised excessively we need to figure out why.
Cortisol dysregulation/hypoglycemia are common problems in sleep disorders. These can be driven by a whole range of different stressors, but for the lifting and fitness population, inflammation from overtraining is one cause that you need to consider. Insufficient calories is another.
If the blood sugar is out of range two hours after you've eaten, then you'd need to investigate your diet. What's called the "first phase insulin response" happens within a couple of minutes of consuming food. This can be dysfunctional due to gastrointestinal issues or early signs of beta-cell problems. And it can be seen in a general way with blood glucose monitoring where the blood glucose stays really high in the first hour and a half after eating.
Another thing to consider is insulin resistance, though in a population which exercises a lot, there's a secondary insulin receptor that helps with glucose transport and it's turned on by exercise. This by itself is a good enough reason to keep lifting as you age.
The other reason it may be high is due to excessive carb consumption. This type of monitoring really can tell you if further investigation would be warranted, though not exactly what's going on since there are many nuances. So, if fasting blood sugar is out of range, then looking at stressors is important. If post-prandial blood sugar is out of range, look at diet.