Thursday, 21 June 2012

Foods that Make you Fat: Bread or Cereal for Breakfast

According to a recent survey, the most popular breakfast items eaten at home in UK are toast and cold cereal.  No wonder 60% of us are overweight.  Bread products and breakfast cereals are cheap to buy and easy to prepare.  Advertising campaigns promote them as being full of 'healthy whole grains'.  Some are even marketed as weight loss products.  So what could be wrong with them? 

It's important to understand that these foods don't cause weight gain due to the calories they contain, but due to their effects on our metabolism. Let's take Special K cereal as an example, since it's advertised as sliming.  It contains 76 grams of carbohydrates per 100 grams, made up of 17 grams of sugars and 59 grams of starch. 

What happens when you load up on lots of starch and/or sugar?   First of all, your body converts these carbohydrates into glucose, also known as blood sugar.  As you chew and swallow your cereal, your blood glucose quickly rises.  Too much sugar in your blood is deadly, so your pancreas releases the hormone insulin to lower it.  Insulin converts some of the glucose into glycogen to be stored in the muscles.  It converts the rest into triglycerides to be stored in the fat cells. 

The more carbohydrates you eat in a meal, the more insulin is needed to lower blood glucose and the longer it persists in your bloodstream.  An important fact about insulin is that it activates fat storage and prevents the body from using fat as energy.  The purpose of insulin is to remove glucose from the blood. The fat cells are essentially locked shut so that glucose gets burned in preference to fat. 

Insulin not only stops you from releasing stored fat, it also makes you hungry.   If you eat a typical breakfast of cereal or bread you may start to get food cravings about two hours later.  In addition, you may feel tired, have difficulty concentrating and lose patience with people or tasks.  This is because  insulin has done its job and your blood glucose has dropped.  Your fat-burning metabolism is still shut down, and there's no longer a readily available energy source for your body.  Time to grab a snack quick! 

But that's not the whole story.  Another hormone is involved.  Ghrelin is manufactured by cells in the stomach and signals the brain to increase your appetite.  When your body produces ghrelin, you feel an urge to eat.  High protein meals suppress ghrelin for hours afterwards.  High carbohydrate meals suppress ghrelin at first, so you feel full after eating.  However, a couple of hours later, ghrelin increases dramatically.  If you eat a breakfast of starches and sugars you may be hungrier mid-morning than you were when you woke up.

Eggs Instead

High carbohydrate breakfasts lead to gain weight in two ways.   They stop you from burning your body fat and they make you crave snacks before lunchtime.  If you're trying to lose weight, what should you eat instead?  Any kind of protein food is a good idea, but I suggest eggs.  It only takes a couple of minutes to prepare them, they're relatively cheap and they've only got around 75 calories each.

In a study published in the journal Nutrition Research, scientists compared the body's response to eating a bagel breakfast or an egg breakfast  containing the same number of calories.  Three hours after breakfast, subjects were presented with a buffet lunch and told to eat until they were satisfied.  They also filled in a hunger questionnaire and a survey about food intake on the day before and after the test breakfast.  Researchers took blood samples from the subjects before they consumed their eggs or bagels and at various intervals afterwards.  

The researchers tested the blood samples for indicators linked to hunger.  The bagel breakfast produced a rise and fall in blood sugar and insulin, whereas blood sugar and insulin levels were more stable following the egg breakfast.  In addition, ghrelin rose significantly more following the bagel breakfast than the egg breakfast. 

The subjects' eating behaviour reflected their blood test results.  Those who ate a bagel breakfast reported more hunger three hours later than those who had eggs.   They also consumed significantly more calories at the all-you-can-eat buffet lunch than the egg eaters.  In addition, the food surveys showed that bagel eaters consumed more calories in total over the 24 hours following breakfast.

Links to research articles

Variations in postprandial ghrelin status following ingestion of high-carbohydrate, high-fat and high-protein meals in males

Consuming eggs for breakfast influences plasma glucose and ghrelin, while reducing energy intake during the next 24 hours in adult men

Personal aside

Back when I was fat,  I used to eat carbohydrate breakfasts like cereal, toast, crumpets, muffins or bagels,  I had the typical mid-morning low blood sugar response.  If I didn't get a snack I would feel tired, weak, confused and irritable.  Now I eat two eggs every morning and I'm good till lunchtime. 

On the other hand, my partner eats a big bowl of cereal every weekday morning and never feels hungry.  Is it due to his metabolism or the fact that he smokes and nicotine is an appetite suppressant?

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