...and does TOO much protein really turn into carbohydrates?
Last week, I made an Instagram reel that upset many people when I mentioned that excess protein just gets converted to carbohydrates and encouraged followers to "just eat bread!"
A quick and witty reel intended to reach my niche market instead reached over 10,000 people (and growing). Diet culture worked at its best in the comments glorifying protein and demonizing carbohydrates, specifically bread, trying to discredit my post. But as a registered sports dietitian with a Master's degree in Sports Nutrition and over 10 years of work experience with competitive athletes, 6+ years specifically counseling female athletes, many of whom struggle with low energy availability, REDS, and disordered eating, I was confident in the accuracy of my post.
Protein's main function in the body is to build; build muscle, bone, connective tissue, enzymes, antibodies, skin, hair, and more! But if the body is in a state of energy deficiency, the ability for protein to build is very difficult. When working with female athletes, I found that many of my clients were eating excessive protein yet losing muscle and strength, experiencing worsening performance, hair falling out, nails being weak, and getting injured. This was happening because despite the high protein intake, they were not consuming adequate total calories or carbohydrates, and sometimes inadequate fat as well. This puts female athletes in a state of energy deficiency and possibly at risk of RelativeEnergy Deficiency in Sport, REDS. To learn more about the consequences of female athletes in a state of low energy availability, please check out my blog post from my old website: Signs of REDS in Female Athletes.
Here is an example of a client I worked with in the spring of 2024. She was a collegiate athlete who, in high school, strongly resonated with an eating disorder and was diagnosed with osteoporosis at a young age. In the last few years, she made huge strides in improving nutritional intake, overcoming her eating disorder, and improving her bone health, verified by DXA scans. However, her menstrual cycle was still inconsistent, and at the time, she had been missing it for 9 consecutive months. She was rehabilitating an injury and preparing for her next competitive season of collegiate cross country but knew she needed to address her missing menstrual cycle. She was still experiencing unhealed injuries and was unable to make progress in her training. Upon reviewing her diet, I set targets for energy availability based on her sport expenditure and set high protein requirements considering her injury and bone health.
Of note, the International Society of Sports Nutrition sets protein guidelines between 1.4-2g of protein per kilogram of body weight (ISSN source). However, due to her unique circumstances of low bone mineral density, I set her goal even higher at 2.5g/kg, which was 16% of her recommended diet composition, with a goal of 54% carbohydrate and 30% fat due to the importance of fats for amenorrhea recovery in female athletes. Even with a very high protein goal, you can see in the graph below that she was meeting far beyond that amount at 140% of her protein goal, or essentially 3.5g/kg. However, only 70% of her carbohydrate and 65% of her fat requirements were being met, putting her total energy at only 79% of her needs. This is the type of client that I had to say: "Excess protein is just turning into carbohydrates anyway, so you might as well just eat the bread!" implying that she needs to focus more on adding carbohydrates to her diet.
The science behind protein turning into carbohydrates is a process called gluconeogenesis. It happens when the body does not have enough carbohydrates and needs to break down alternative fuel sources to maintain blood glucose. This is a life-saving process during periods of starvation and is likely rare in the general public following a standard American diet. However, the reality is that female athletes who are under-fueling are placing their body in a metabolic state that follows that of starvation.
"Prolonged fasting or vigorous exercise depletes glycogen stores, making the body switch to de-novo glucose synthesis to maintain blood levels of this monosaccharide. Gluconeogenesis is the process that allows the body to form glucose from non-hexose precursors, particularly glycerol, lactate, pyruvate, propionate, and glucogenic amino acids."
"Glucogenic amino acids enter the gluconeogenesis pathway via the citric acid cycle The first step is the deamination of the glucogenic amino acids into α-ketoacids, which are substrates in the citric acid cycle.
Melkonian EA, Asuka E, Schury MP. Physiology, Gluconeogenesis. [Updated 2023 Nov 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK541119/
The biochemical fingerprint of short-term LEA [low energy availability] can be observed in the context of acute nutrient deprivation, which is well known to trigger a classical physiological cascade. Fasting- and energy-deficiency induced hypoglycemia can be partially prevented, owing to reduced insulin production and elevated glucagon, epinephrine, and cortisol secretion secondary to starvation. However, carbohydrate and glycogen stores are soon depleted, and gluconeogenesis takes over using amino acids and glycerol for 24 to 48 hours, followed by ketogenesis. After a few days, a branched-chain amino acid surge triggers the shift to lipid metabolism and ketogenesis, as attested by elevated cortisol, free fatty acids, β-hydroxybutyrate, and ketone body concentrations. Once adipose tissue (AT) reserves are depleted, the lipolytic metabolic shift is followed by protein catabolism.
Angeliki M Angelidi, Konstantinos Stefanakis, Sharon H Chou, Laura Valenzuela-Vallejo, Konstantina Dipla, Chrysoula Boutari, Konstantinos Ntoskas, Panagiotis Tokmakidis, Alexander Kokkinos, Dimitrios G Goulis, Helen A Papadaki, Christos S Mantzoros, Relative Energy Deficiency in Sport (REDs): Endocrine Manifestations, Pathophysiology and Treatments, Endocrine Reviews, Volume 45, Issue 5, October 2024, Pages 676–708, https://doi.org/10.1210/endrev/bnae011
In my client's example above, consuming 140% of her protein goal wasn't hurting her, but eating only 70% of her carbohydrate goal was. It was imperative that she add carbohydrates, fat, and, therefore, calories to her meals. She was training 2+ hours a day for about 6 days a week and not seeing progress in restoring her menstrual cycle or recovering from her injuries. I gave her the option to simply add carbohydrates to her meals, or, if struggling with fullness, focus slightly less on protein while adding carbohydrates and fats. For example, she often ate 5-6 ounces of protein at a meal. In order for her to balance her nutrition and fuel with more carbohydrates and fats, I suggested she consume 3-4 ounces of protein at each meal while increasing her carbohydrate and fat portions.
To be clear, the problem wasn't that she was consuming too much protein but rather inadequate carbs and fats for her needs. Her body, in a state of REDS and low energy availability, was likely turning that excess protein into calories that she could use via gluconeogenesis.
In a different population, perhaps those struggling with obesity, metabolic syndrome, or type 2 diabetes, it is possible that consuming a high protein, low carbohydrate diet is helpful to their health. Gluconeogenesis may also be occurring in these situations, but it may be helpful to fix the health problems that this population is experiencing by reducing insulin response and preserving as much muscle mass as possible while in a catabolic state. However, female athletes need to remember that it is not good for performance to be in a catabolic state and that long-term energy deficiency can hurt hormones, health, and performance in athletes. Female athletes want adequate carbohydrates to fuel their muscles, enhance recovery, and use insulin as an anabolic hormone to build, repair, and adapt positively to training.
So yes, some female athletes are focusing too much on protein when they actually need to increase carbohydrates and fats for a balanced performance and health-enhancing diet. With that being said, protein is still very important! To ensure you are eating enough protein, consider using the ISSN guidelines:
Endurance exercise 1-1.6g/kg/day
Elite endurance athletes should be on the higher end of the range due to increased oxidation of branch chain amino acids
Strength/power exercise 1.6-2g/kg/day
The higher end of the range is needed for beginners. Some research suggests that protein requirements actually decrease as one becomes more trained due to biological adaptations
Intermittent sports (ie: soccer, basketball) 1.4-1.7g/kg/day
Using the above guidelines, its reasonable for a sample female athlete of any sport weighing approximately 150 pounds to consume 1.6g of protein per kilogram body weight, which equates to approximately 110 grams of protein per day. A sample diet could inlcide:
Breakfast:
2 slices of while grain or seed bread (6-10g protein)
2 whole eggs (12g protein)
1/2 cup whole milk, alone or in coffee (4g protein)
1 cup cut fruit
1 tbsp cream cheese or butter
Snack/Pre Workout:
6 dates th
Post Workout Recovery:
1/2 cup 2% greek yogurt blended into a smoothie with (11g protein)
1 tbsp ground flaxseed (1g protein)
1 banana
1/2 cup strawberries
1 cup soy milk (8g protein)
Lunch:
Whole wheat tortilla wrap filled with (5g protein)
3 oz chicken breast (21g protein)
1 tbsp mayo
1/4 cup arugula and sliced tomato
Side of 10 baby carrots with
1/4 cup hummus (4g protein)
1 cup mini pretzels
Snack:
Apple
1oz almonds (6g protein)
Dinner:
3.5oz salmon (25g protein)
1 cup white rice
5-10 spears Asparagus (1-2g protein)
1 tbsp olive oil used in cooking
1 thick slice sourdough bread and butter (6g protein)
This sample is approximately 111-116g protein. For those needing more protein you can increase the portion of protein foods or add more protein sources! There are many female athletes who need 150g, 180g, 200g of protein or potentially more! But even still, a balance with energizing carbohydrates is key. This sample above also provides ample carbohydrate and fats at nearly 50% and 30% of the diet, respectively (your needs may be different, more or less!).
When figuring out what foods to eat to reach your protein goal, it's important to remember that protein is found in more than just meat. The sample meal plan above showed that protein can be found in whole grains, nuts, dairy products, beans, and soy. Surprisingly, some vegetables, like broccoli and asparagus, can be a small source of protein!
Ps...did you notice bread was allowed on this balanced sample meal plan? 😉 That's because if you want protein to do its job at the building, then you need to eat adequate carbohydrates to energize. Otherwise, without enough carbs, all that extra protein just gets converted into glucose anyway!
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