As most people are probably aware, Americans are eating less fat but are fatter than ever! One likely culprit is the fact that most people have replaced fat with high GI foods such as "low fat" cookies, cakes, rice cakes and other high GI foods.
Some research has even found the GI of food can actually alter the eating behavior all day long. One recent study examined how the GI affected eating behavior in obese teenage boys (Ludwig, D.S., et al., 1999).
The boys consumed either a high, medium or low GI meal at breakfast and lunch. They then measured how much the boys ate for a 5-hour period after lunch. Each of the meals contained the same number of calories.
Amazingly, the study found food intake was 53% greater after the medium GI meal and a whopping 81% greater after the high GI meal when compared to the low GI meal.
As one would expect, insulin levels were dramatically higher after the high GI meal. The study showed that a single high GI meal could effect how many calories a person will eat many hours later. The reason for this is most likely the effect of the high GI meal on blood sugar (Roberts, S.B., 2000).
As mentioned, the study found the insulin levels of the high GI meal were much higher than the other meals. When insulin rushes in to lower blood sugar after a high GI meal, the effect can be low blood sugar shortly after, thus the body senses the low blood sugar sending out the hunger signal.
Eating low to moderate GI carbs throughout the day keeps steadier blood sugar levels and thus the body senses that adequate food and carbohydrates are coming in. The feedback pathways controlling hunger and appetite (no they are not the same thing) is incredibly complex and beyond the scope of this chapter. Suffice it to say, blood sugar levels and blood sugar levels effects on insulin is one key feedback mechanism the body uses to sense incoming nutrients diverting those nutrients where needed.
There are numerous studies that find eating high GI foods is associated with greater bodyfat levels (Morris, K.L.,1999) and some animal studies have found feeding high GI foods to animals causes them to gain bodyfat. When you understand the role of insulin in human metabolism, it does not take a PhD in biochemistry to see why this would happen.
One thing is clear, the GI of the carbs you eat will be a factor in how much bodyfat is ultimately produced from the meal and the spike in insulin you will produce (Pawlak, D.B., et al, 2001; Marques-Lopes, I., et al, 2000; Ludwig, D.S., et al, 1999).
You know those low fat cakes you were so happy about? Throw 'em out! One important caveat to remember. Calories also matter and although it may be possible to eat greater amounts of low GI carbs vs. high GI carbs without problems, it's far from a free for all excuse to stuff oneself with carbohydrates.
The body can only 'burn' and store so much carbohydrates as glycogen. After that, increased body fat will be the result. The trick is to eat the correct amount - and types - of carbs to fill glycogen levels and fuel workouts and daily activities, while making up the other calories in healthy fats and proteins, as will be covered shortly.
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