The glycemic index (GI) is a scale that shows how quickly a given food raises blood glucose levels after eating. The higher the GI, the faster and more intense the glucose spike – which can lead to sudden insulin responses, post-meal sleepiness, and over time – insulin resistance.
For those following a keto or low carb diet, the GI is a helpful tool to choose foods that support fat metabolism and keep blood sugar stable. But beware – GI doesn’t tell the whole story, and not all high-GI foods are automatically bad.
What exactly is GI?
The glycemic index measures the effect of 50 grams of digestible carbohydrates from a specific food on blood sugar, compared to pure glucose (which has a GI of 100).
We usually divide foods into three GI categories:
- Low GI (0–55) – slow sugar release
- Medium GI (56–69) – moderate release
- High GI (70+) – fast sugar spike
What affects a food’s GI?
- Processing level – more processed = higher GI
- Cooking time – overcooked foods tend to have higher GI
- Fat and fiber content – they slow down digestion and lower GI
- Temperature – cooled foods often have lower GI (e.g. cold potatoes vs. hot)
- Acid content – vinegar or lemon juice can reduce the GI of a meal
How to use GI in practice?
- Base your meals on low GI foods – e.g. broccoli instead of potatoes
- Combine higher GI foods with protein, fats, and fiber to slow the sugar impact
- Always look at the whole dish, not just single ingredients
- Avoid instant and overprocessed foods
- Use acidic touches like lemon juice or vinegar to lower the glycemic load
But remember – GI isn’t everything!
The GI tells you how fast glucose appears in your blood, but not how much. That’s why foods like:
- Watermelon – high GI, but low in carbs overall → small actual sugar load
- Cooked carrots – relatively high GI, but usually eaten in small amounts
That’s why it’s helpful to also understand the glycemic load (GL), which takes portion size into account – but we’ll cover that in a separate article.
Low GI foods at a glance:
See the infographic below for a list of low glycemic index foods perfect for a keto or low carb diet.
– with flavor, Pozi von Cuks
