Refined carbohydrates can cause an immediate and drastic increase in blood sugar levels, followed by a drastic drop back to normal or below normal. If you were to chart it, it would look like that first (steep) hill on a rollercoaster that goes way up and then way down.
Complex carbs, on the other hand, digest slowly, so the increase and decrease are not as steep or dramatic. If you were to chart the digestion of complex carbs, it would look like a slow Sunday drive over a small gradual hill. To recap, refined carbs create a fast, intense, and stressful glucose response in the body (like a rollercoaster), whereas complex carbs create a steadier, less intense, non-stressful response in the body (like a Sunday drive).
Regarding fuel efficiency, it’s important to aim for the Sunday drive—to choose carbohydrates that will not cause dramatic spikes and falls in blood sugar levels. As we talked about in the last chapter, these constant spikes and falls can lead to weight gain as well as many other serious health issues over time, including insulin resistance and hypoglycemia.
But how can you tell a rollercoaster carb from a Sunday drive carb? By using what’s known as the glycemic index (GI). The GI Index is a measuring system that indicates what kind of glucose response a food will initiate in the body. Each food is ranked on a scale from 0-100. Foods low on the GI scale (45 and below) are typically complex carbs that contain fiber and protein, and so they release glucose slowly and steadily (Sunday drive). Foods high on the GI scale do not have as much fiber and protein, and so they release glucose rapidly (rollercoaster).
For example, a bowl of corn cereal ranks around 85 on the GI index, but a raw apple ranks around 34, even though both contain approximately 25 carbohydrates per serving. The cereal, though, is processed in a factory and stripped of most of its nutrients, so it creates a dramatic spike in blood sugar (rollercoaster). The apple, on the other hand, still contains all its natural fiber and protein, so it is digested slower and creates a less dramatic increase (Sunday drive).
Another example: mashed potatoes rank around 90 on the GI index, but chickpeas rank around 20, even though a serving of each contains approximately 30 carbohydrates. The reason: chickpeas are often just rinsed and canned, and then eaten raw, so they still contain their fiber and protein. Potatoes, on the other hand, are first peeled of their skin (which contains fiber and protein), and then are boiled at high temperatures causing a loss of enzymes and nutrients. So, the end product is a rollercoaster carbohydrate high on the GI index. (The same can be true for the apple, though, if it is skinned and cooked at high temperatures to make applesauce. In that case, it will rank much higher on the GI index.)
Now, the GI scale is not a perfect system because you also need to take into consideration where the entire meal ranks on the scale. A high GI food like potatoes paired with protein-rich grilled salmon has a collectively lower ranking than just eating mashed potatoes by itself. But it’s still higher than eating salmon with a side salad, instead of potatoes.
It’s also important to consider where your day falls on the scale. Many people get stuck on what I call “the all-day rollercoaster.” They eat white bread toast for breakfast, a white bread sandwich for lunch, and rice or dinner rolls for dinner. In between, that they have crackers, pretzels and chips for snacks, and soda and sugar-spiked coffee for beverages. Throughout the day their fueling system runs like a crazy thrill ride with fast, intense ups and downs… which explains why they’re exhausted at the end of the day. If this is you, friend, my advice is to get off the rollercoaster. Avoid high GI foods—especially while trying to rebuild the temple fueling system. But if there are times when you cannot avoid these foods, it is best to pair them with other protein or fiber-rich foods at least to slow digestion some.