Over-Sugared Children = Over-Fat Adults?

One day in my mid-teens I discovered a shocking truth – people drink straight chocolate milk!

Yes! I was stunned! After years of having my chocolate milk mixed with regular milk (about 50% chocolate and 50% regular) I discovered the obvious: you can drink chocolate milk straight.

My entire childhood was filled with diluted chocolate milk. To this day drinking straight chocolate milk seems so daring and way too sweet.

Why do I bring this up?

Well, how much does your childhood exposure to sugar matter to you now as an adult? Is there a such thing as a childhood environment that creates obesity in adults?

This week’s review article examines a short-term sugar exposure in childhood and adolescents and how that affects things you’d think would make people obese — such as activity levels, glucose tolerance, preference for sugar, and body weight.

Frazier CR, Mason P, Zhuang X, Beeler JA. Sucrose exposure in early life alters adult motivation and weight gain. PLoS One. 2008 Sep 17;3(9):e3221.

Methods

Okay, I picked a study that uses mice for its participants. Yes, I know you are not a mouse, but not many parents are okay with having their 1 year old taking extra sugar just to see what happens. And it would take a while to find out what happens when they’re adults.

But since this study is done on mice and not people, we have to be careful and take the results with a grain of salt (or in this case, sugar).

Mice on sugar

Fifteen mice were given unlimited amount of sugar (in 20 mg tablets) starting when they were 3 weeks old, until they were 7 weeks (7 mice) or 10 weeks old (8 mice). Thus:

• 7 mice were on sugar for 4 weeks.
• 8 mice were on sugar for 7 weeks.
• There was another control group of mice that didn’t get any sugar.

All the mice had unlimited access to food (mouse chow) and water.

Mouse behaviour

To figure out whether sugar affected mouse behaviour, the researchers did a few tests:

1. Open field test – mice running around in an open field (well more of an open plastic box 40 cm x 37 cm x 37 cm high). This tested the mice’s activity level.
2. Wheel running – same wheel your hamster had when you were little. Same thing here: by finding out how far the mice run on the wheel, you have an idea of their activity level.
3. Operant test – aka the “how much work will the mice do for sugar?” test. The mice have to press a lever to get sugar, but there’s a catch – the number of presses keeps going up. The test starts at 1 press, and increases from there to 35. This test was done with other food available and without.
4. Sucrose preference– mice had access to water (no sugar) and one sugar solution (0.2%, 5%, 10% or 15% in concentration). Every 4 days a different concentration of sugar that was accessible to the mice was changed.

Other tests – Mouse glucose tolerance & dietary challenge

This test is very similar to human glucose tolerance except blood is taken from the tail.

After a 21 hour fast the mice were given 2g/kg dextrose in 0.9% saline glucose challenge (I’m guessing this was done intravenously otherwise they wouldn’t have bothered with the saline). Blood was checked at 30, 65 and 90 minutes. And yes, mice can get diabetes.

In the next test mice were given their regular food (mouse chow) and access to various Nestlé chips. Yes, chips — you know, chocolate chips, white chocolate chips, butterscotch chips, peanut butter chips), etc. (Wonder if Nestlé knows about this somewhat dubious endorsement of their products.)

Note: mice really like chocolate, so in a pinch if you’re trying to catch a mouse and are willing to give up your chocolate bar….

Anyway, the mice were weighed before the chip feast began and every week after that for three weeks.

Results

First interesting finding: The mice given sugar freely in their childhood and teens (3-10 weeks old) didn’t weigh any more than their brothers and sisters that didn’t get extra sugar.

So extra sugar in their youth didn’t lead to weight gain later on – remember the mice only got unlimited sugar for that 4-7 week period and after that there was no difference in food.

Does early sugar exposure change physical activity?

Comparing the open field test and the wheel running test there was no difference in how active the two groups were – so early sugar exposure didn’t make the mice more or less active.

What gets really interesting is when the researchers put a reward with activity. When there is sugar available as a reward for pressing the lever then things change.

You’d think that the mice with early exposure to sugar would be addicted to sugar and, like little furry heroin addicts, press on the lever indefinitely until they got their sugar fix, but that didn’t happen. In fact, in every case (other food available or not) the early-sugar-exposed group didn’t put as much effort into the food access (lever presses) as the control group.

So no difference in activity until there is a reward of sugar. Sugar seems to be a bigger incentive for the control group either that or the other mice are less motivated by sugar. Either way it seems a little counterintuitive.

The researchers explain the differences by saying that the mice exposed to sugar early on are less willing to put effort into getting the reward. If the sugar is readily available they will consume it (as with the sucrose preference test). So it’s more a matter of work involved than not wanting the sugar.

Glucose tolerance & chocolate chips

With all the talk of childhood diabetes in people you’d figure that the mice exposed to unlimited sugar early on would have elevated blood glucose when challenge, but nope.

There was no difference in glucose tolerance between control mice and mice given unlimited sugar – weird. It could go back to the short exposure to sugar and that since then the mice were given healthy food and were active.

So far unlimited early sugar exposure doesn’t seem like a bad thing.

Could it be that unlimited sugar as a child isn’t so bad? Can we dispense Baby’s First Froot Loops with abandon?

Nope.

The dietary challenge (aka the gorge-on-chocolate-chip test) found that there was a big downside to early sugar exposure – vulnerability to obesity.

If the mice were on a healthy diet then there were no difference, but once high sugar and high fat food was introduced then there were differences. With the same amount of chocolate chips (the researchers weighed all the food) the early-sugar-exposed group gained more weight than the control.

How much more? The female mice gained 17% more weight after 3 weeks than their control sisters and the male mice gained 12% more than their control brothers. Remember: this is with the same amount of chocolate chips.

In other words, despite the same total calorie intake, mice who were exposed to sugar early in life gained more weight when eating high-sugar/high-fat foods than the control group that didn’t get early sugar.

Conclusion

So on one hand, we have no differences: no differences in weight, glucose tolerance, or activity. We also have less motivation to find sugar in the early-sugar group. So, the early-sugar mice aren’t less active or more nibbly than their control group peers.

But yet, on the other hand, the early-sugar-exposure mice seem to be excellent weight gainers when compared to their normal peers, given an obesegenic (high sugar/high fat) diet.

What’s up? This finding points to changes in metabolism. The early-sugar-exposed mice have, in essence, become little mousy fat factories. They’re better at gaining fat when given a fat-stimulating diet.

The authors suggest that a “thrift genotype” is altered – meaning that early exposure to unlimited sugar turns on certain genes that are responsible for storing extra calories. So, if mice (and possibly people) are given the same amount of high fat/high sugar food, the mice with the thrift genotype save more calories in the form of fat.

Are people overweight because of nature (genetics) or nurture (environment)? Well, that makes the assumption that two don’t influence each other.

The truth is that nature influences nurture and vice versa. This study shows how early experiences change how food is processed in adulthood.

If you’re interested in knowing more about genes and environment you might want to read an interesting book called Nature via Nurture: Genes, Experience and What makes us Human by Matt Ridley. It does a very good job at exploring how nature and nurture are intertwined and not subservient to the other.

Bottom line

In mice, being exposed to sugar early in life primes the body to store calories from high fat/high sugar foods and leads to weight gain. (And possibly, they will join the legion of Fatmouse.)

These findings aren’t definitive for humans, but they are suggestive.

If your parents didn’t dilute your chocolate milk, are you doomed? No.

The good news is that even if exposed to unlimited sugar as a child, it appears that a healthy diet still helps prevent weight gain.

Just skip the baking aisle when you’re grocery shopping.