Sunday, May 25, 2014

Why am I always hungry? Food quality vs quantity

Could it be that your past eating habits are making you hungry now?

Have your fat cells turned on you, hoarding your calories so that you feel hungry, despite having eaten enough to meet your actual energy demands?

photo: AllFunnyImages

It may that eating a low-quality diet changes the behavior of fat cells and thus has a greater influence on hunger and weight gain than the sheer number of calories we take in and burn off.

That is the hypothesis behind a new study on overeating and weight gain published in the Journal of the American Medical Association (JAMA).

Here's the idea:

Eating highly-processed carbohydrates -- such as chips, crisps, fries, cookies, sodas, sugary cereals, and refined white bread -- leads our bodies to produce more of the hormone insulin than we would eating veggies, meats, and whole grains (applause from the Paleo crowd, whose point on minimizing our junk food intake is spot on).

Digestion & insulin

When we digest a food with carbohydrates, the resulting materials with sugars (glucose), proteins, and fats spread through the blood from the intestines to the rest of the body to give cells energy to function.

cupcake with your tea?
photo: RubMint
Insulin is a hormone released by our pancreas that regulates our metabolism of sugars and fats. When sugar enters the blood after we eat, the pancreas released insulin to tell the cells to let in glucose, which the cells use for energy.

If we don't produce enough insulin, which happens with diabetes, these cells don't absorb the glucose, so the body starts using its fat to produce energy and loses weight. The associated high blood sugar ultimately causes serious complications.

Release of too much insulin causes muscle, fat, bone and other cells to absorb glucose from the blood and use that, rather than stored fat, as their source of energy.

The body needs some of that energy circulating, and when too much glucose is trapped in fat tissue, it can't be used by other organs. So, in its wisdom, the body tries to save energy.

The lack of glucose and fatty acids in the blood encourages the body to store, rather than burn, calories. This makes us feel hungry, reduces the number of calories we burn for any given amount of exercise, and makes us tired.

So even if we've consumed enough calories, they are trapped in the fat cells instead of doing their job producing energy for the whole body.  Hey!

The guilty party here appears to be a high glycemic index (GI) diet - one with a lot of foods that digest rapidly and spike blood sugar quickly. These tend to be highly processed. Meat and fats don't contain carbohydrate so don't even appear on the scale. Carbs with low GI levels tend to retain more fat and/or fiber, while those with high GI levels have more simple sugars.

From, here are a variety of carbohydrate foods with low, medium, and high GI levels:

Low GI Foods (55 or less)

  • 100% stone-ground whole wheat or pumpernickel bread
  • Oatmeal (rolled or steel-cut), oat bran, muesli
  • Pasta, converted rice, barley, bulgar
  • Sweet potato, corn, yam, lima/butter beans, peas, legumes and lentils
  • Most fruits, non-starchy vegetables and carrots

Medium GI (56-69)

  • Whole wheat, rye and pita bread
  • Quick oats
  • Brown, wild or basmati rice, couscous

High GI (70 or more)

  • White bread or bagel
  • Corn flakes, puffed rice, bran flakes, instant oatmeal
  • Shortgrain white rice, rice pasta, macaroni and cheese from mix
  • Russet potato, pumpkin
  • Pretzels, rice cakes, popcorn, saltine crackers
  • melons and pineapple

I am a really big fan of carbohydrates and hate as much as anyone the idea of a low-carb diet, so I'm happy to see that most of the carbs I eat are low or mid-level GI carbs. Except bagels!  Arrggh.

do anything for cookies   photo: RubMint
I already pretty much knew chocolate chip cookies would make the no-go list...

Does any of these ring a bell to you?

It does seems that it's the heavy processing of modern junk food, creating the low glycemic index diet, that is the big problem, but any processing increases GI level. Juice has a higher GI than raw fruit, and more cooking = higher GI level for the same food.

The GI level isn't perfect in terms of diet choices, as it doesn't consider how much carbohydrate is in a food (watermelon is high GI but low in actual amount of carbohydrate, so have another slice!), but it is a good guideline.

The study was done on laboratory rats, not people, but the results are considered to be similar. The increased insulin produced by the rats caused more synthesis of fatty acids into fat tissue and converted more glucose into lipids that encouraged fat deposition, especially around the belly.

So rats fed diets with a high glycemic index gained more fat, and these various processes continued in the lab rats, even once their diets were calorie-restricted, so their junk food binges lived on.

guess who's been hittin' the junk food?
photo: foodnavigator

Takeaway message:

The quality of the food you eat may be more important than the quantity.

Learn more

This New York Times article which introduced me to this topic and clearly describes the ideas of weight setpoint, insulin absorbtion, the study methods, and its findings (by the authors of the original paper)

The original paper in JAMA that prompted the NYT write-up (for you biologists out there)

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