Understanding Glycemic Index, Glycemic Load & Carb Timing

Rahul Garg

 | 1 minute to read
Nutrition
If you go online and do even a basic research about carbohydrates and dieting, chances are you’ve come across three terms: GI, GL and carb timing. According to advocates of a low carb diet, these three factors prove that fewer carbohydrates in your diet equals faster fat loss. But is that true? Let’s understand what these terms actually mean - with the help of science.

Understanding Glycemic Index Glycemic Index (or simply GI) is a food ranking system which indicates the rate at which the food gets converted into glucose and ultimately used as energy. In simple terms, it tells us how rapidly the food will be digested & absorbed and how quickly the blood glucose levels will elevate. In this principle, the foods are ranked from GI of 1 to 100 where 1 indicates the food which digests the slowest and 100 indicates foods which digests the fastest. It is calculated as under: GI = blood glucose level after ingestion of product containing 50g divided by blood glucose level after ingestion of 50g glucose What It Means A low GI food is preferred for higher satiety and a high GI food is preferred for instant supply of energy due to readily available blood glucose. However, GI of mixed foods (a low GI food or fats mixed with high GI food) will have a balanced GI and will not be a valid predictor of hunger, appetite & satiety. Also, GI doesn’t consider the amount of food consumed, making it an inefficient parameter to decide if the food consumed is “good” or “bad” and should not be giver high significance while designing a diet. That’s why we need to also look at the Glycemic Load. Understanding Glycemic Load Glycemic Load (or simply GL) shows how much the blood glucose levels will rise after someone has consumed a particular amount of carbohydrates. This principle compensates for the shortfalls of the Glycemic Index Principle, since it considers the amount of food ingested by the person (and not just the rate of its conversion into glucose). What It Means A low GI food, if ingested in higher quantity, might give a higher insulin spike as compared to a high GI food ingested in relatively lower quantity. It is calculated as under: GL = Carbohydrate content (g) x Glycemic index divided by 100 So, if 100g carbohydrate with a GI of 40 is consumed, the GL would be 40 (100x40/100). Alternatively, if 50g carbohydrate with a GI of 80 is consumed, the GL would again be 40 (50x80/100). This clearly shows that the blood glucose spike will be similar in both these cases irrespective of the total carbohydrate content and different glycemic index. Hence, GL is a better parameter while designing a diet (especially for people suffering from Type 2 diabetes and obesity). Understanding Carb Timing Does the timing of carbohydrate intake matter? Will it help with energy balance (calorie deficit/ surplus for losing/gaining weight) and performance improvement or even improve your sleep quality? Let’s understand this. 1. Carbohydrate intake timing & weight loss It’s commonly believed that you should not consume carbohydrates at night if you want to lose weight (even if you are in a calorie deficit). Several myths are associated with it, the most famous one being that you should not eat rice in dinner. We have to understand that a gram of carbohydrate will give 4 kcal energy, irrespective of whether it was eaten at 4 PM or at 8 PM. One of the most common myths is that sleeping metabolic rate is slower than resting metabolic rate. However, studies show that leaner individuals have a higher sleeping metabolic rate. For an obese person, the sleeping metabolic rate could be slower but even then, it won’t make much of a difference if the person is in a calorie deficit. We can therefore conclude that the timing of carbohydrate intake is irrelevant if your total daily calorie intake is in line with your fitness goal. 2. Carbohydrate intake timing & performance improvements Glycogen depletion is a major limiting factor during moderate to high intensity endurance sports. There are numerous research studies which show that carbohydrates are ergogenic and if they are consumed right before or during high intensity exercises (exercises lasting for 1 to 2.5 hours or even longer), they will improve performance by maximizing endogenous glycogen stores. But if the goal is to improve fat oxidation (use of body fat as a source of energy) and mitochondrial efficiency and the performance is not compromised by limiting carbohydrates, training with lower carbohydrate intake can help. 3. Carbohydrate intake timing & their effects on sleep quality Research also shows that a high GI meal 4 hours before bed-time helps significantly reduce Sleep Onset latency (time taken to go from a state of awake to fully sleeping) & a carbohydrate rich diet meal even helps improve the duration of sleep in obese individuals. This is vital since lack of sufficient sleep may produce a catabolic state in which fat loss reduces and loss of muscle mass goes up (in calorie deficit) coupled with increased hunger. Hence, a good night’s sleep is important during the fat loss journey and consuming carbs for dinner helps do that. Takeaway: 1. GI is not an ideal parameter to decide on foods while designing a diet. 2. GL overcomes shortcomings of GI by considering the quantity of carbohydrates ingested and is a good parameter while choosing foods & designing a diet. 3. Consuming carbohydrates before bed time does not mess up with the weight loss journey as long as you’re in a calorie deficit. 4. Carbohydrate intake before or during high intensity endurance sport helps improve performance. 5. Carbohydrate intake before bed time also helps improve sleep quality, and subsequently aids the fat loss journey (assuming the person is in a calorie deficit). References: 1. Y. Niwano 1, T. Adachi, J. Kashimura, T. Sakata, H. Sasaki, K. Sekine, S. Yamamoto, A. Yonekubo, S. Kimura. Is glycemic index of food a feasible predictor of appetite, hunger, and satiety? J Nutr Sci Vitaminol (Tokyo).2009 Jun;55(3):201-7. doi: 10.3177/jnsv.55.201. 2. https://academic.oup.com/jn/article/136/10/2506/4746688 3. https://pubmed.ncbi.nlm.nih.gov/11896493/ Sleeping metabolic rate in relation to body mass index and body composition 4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7352659 Glycemic Index (GI) or Glycemic Load (GL) and Dietary Interventions for Optimizing Postprandial Hyperglycemia in Patients with T2 Diabetes: A Review 5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5240084. The effects of meal glycemic load on blood glucose levels of adults with different body mass indexes. 6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2951287/ Insufficient sleep undermines dietary efforts to reduce adiposity 7. https://pubmed.ncbi.nlm.nih.gov/24456339/ Effects of a carbohydrate-enriched night meal on sleepiness and sleep duration in night workers: a double-blind intervention 8. https://pubmed.ncbi.nlm.nih.gov/17284739/ High-glycemic-index carbohydrate meals shorten sleep onset 9. https://pubmed.ncbi.nlm.nih.gov/25970669/ Performance enhancement by carbohydrate intake during sport: effects of carbohydrates during and after high-intensity exercise 10. https://pubmed.ncbi.nlm.nih.gov/23846824/ The use of carbohydrates during exercise as an ergogenic aid 11. https://pubmed.ncbi.nlm.nih.gov/1895362/#:~:text=Carbohydrate%20intake%20should%20not%20be,%2D60%20g%20h%2D1. Timing and method of increased carbohydrate intake to cope with heavy training, competition and recovery 12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6566225/ Carbohydrate Availability and Physical Performance: Physiological Overview and Practical Recommendations
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Deepthi Unnikrishnan

informative article.

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