Nutrition that makes sense at Shape Up Fitness & Wellness Consulting

Long-term effects of a high carbohydrate diet on your health & performance

  • A High carb  diet (> 70% of intake) can lead to insulin resistance
  • A high carb diet can lead to additional fat gain
  • A high carb diet can increase performance in endurance athletes
  • A high carb diet will lead to increased water retention and could lead to loss of performance
  • Say goodbye to your teeth
  • You are more hungry
  • A high carb diet should be an intervention for performance reasons and not be maintained throughout the year.

Let’s take it apart:

High carb diets (> 70% carbohydrate intake)  followed for a prolonged period of time lead to higher body fat percentages and chronically elevated insulin levels. Choosing to follow such a diet should be restricted to very specific people with specific goals.

Insulin Resistance

Insulin is responsible for transporting blood glucose to muscle cells and fat cells. If we have chronically elevated glucose levels our muscle cells can become more insulin resistant. In return our body produces even more insulin which can lead to a burnout of the insulin producing cells in your pancreas. Congratulations, you just have become a diabetic.

Fat Gain

Our liver and muscle cells can only store a small amount of glycogen (transformed glucose molecules) compared to our capacity to store fat. When on a high carbohydrate diet our body will transform the extra glucose into fat which could lead to that unwanted spare tire around your waist.

Performance Increase or Decrease

It seems like I have two contradictory statements above. One claims that a performance increase is possible, while the other claims the opposite. Now, which is it? That totally depends on you and your sport. Endurance athletes utilizing a high carb diet do so because they want to maximize their glycogen stores for their sport. Having full glycogen stores enables them to perform at a higher level for a longer period of time. The problem is that one 1g of glycogen is stored with 2 g of water. Before you know it, you can have 1-3 lbs of additional water weight which could reduce your performance since you have to haul it around. You will have to find your personal optimum and see what works best for you.

 Hunger & Teeth Decay

Fat and protein stimulate a feeling of satiation better than a high carb diet. This has to do with how long food takes to digest, stomach filling, hormone stimulation by foods etc. Diets higher in fat and protein have a tendency to leave people more satisfied for a longer period of time.

In addition a diet high in carbohydrates almost always consists of highly processed sugary foods (yes, your larabar is part of that, at least when it comes to sugary). Your teeth are under constant assault and your dentist is happy to book his next vacation on your dime.

So what should you do?

If you are an endurance athlete who seeks out performance improvement and would like to avoid some of the negative impacts mentioned above, then you want to reduce the carbohydrate intake to 55% and increase the fat and protein intake. Make sure that the carbohydrates you take in are minimally processed. Then, 3-4 days ahead of your competition you can switch to a high carb diet with 70% carbohydrate intake. If your event is shorter than 90 min then don’t worry about carb loading. It won’t be necessary!

Let me know if you want us to help you with your fitness and training goals. Check out our specials at Charlotte Personal Trainer

Have a great day,



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