Blog Directory - Blogged foodliterate: December 2008

Sunday, December 14, 2008

Random Thoughts: Shelf Life

At the request of a commenter, this week's topic is something that if often asked of me & I can't believe I haven't written about it before now. I think a lot of the confusion happens because there are different terms on packages: best by, use by, sell by. Hopefully I can shed a little light on the topic.

The shelf life a product can best be described as a food quality issue. The manufacturer runs tests and determines how long a product remains in good, sellable condition (still maintains taste, color, appearance, nutrients, viscosity, etc). Expiration dates are about food safety; after this date the product may have a microbial count or species that renders the product unsafe for consumption.

The kinds of dates you will see on packages are:
  • Best before/best if used by - these are food quality dates, not food safety
  • Sell by - this is a food quality date & is for the retailer to manage stock rotation
  • Use by - this is a food safety date, it is the last recommended date for consumption while the food is at peak quality
  • Closed/coded date - these are lot codes used by the manufacturer for recall purposes

To further complicate matters, not all food that has hit its use by date is unsafe or of poor quality and not all food still within its use by date is ok or safe. How a product is handled has a lot to do with both its quality and safety. For example, a refrigerated product that has not been opened and has been held under 37*F may still be perfectly fine to eat after its use by date, while the same product opened and left on the counter every morning may be bad well before its printed use by date.

I can share some guidelines for the more common items often in question:

Milk - the packaging has a sell by date. If held under the recommended storage conditions (less than 37*F) it should be fine to consume for 5 days after its sell by date.

Eggs - if the carton has a USDA shield then there will be a mandatory pack date on the packaging (there may also be a voluntary sell by date) which is a 3 digit Julian code (Jan 1 = 001, Dec 31 =365). If there is a sell by date, it can be for no more than 45 days from the pack date. But eggs have a remarkable shelf life and are good for 5 weeks in the refrigerator; probably longer. The whites will thin out making sunny side up & hard boiled eggs not as desirable, but they are not a safety concern.

Canned Foods - typically don't have a date (other than closed/coded) on their packaging, but the rule of thumb is they are probably good for 2 years as long as they are not leaking, are not rusting and not bulging. It is best to use them within 1 year and hold them in a cool (less than 75*F) area.

Meats - best to eat or freeze within 2 days of purchasing, especially ground or processed meats. Meat has a pretty short refrigerated shelf life, but much longer frozen. Ground meat keeps in the freezer for 3 months, pork for 6 months, and whole meat & chicken for 12 months.

A good place to find additional shelf life information can be found here and here. I always recommend erring on the side of caution. Your nose knows - use it. If something smells funny or funky - don't eat it. Same goes with what you see; if liquid that was clear is now cloudy, or your lunch meats take on a iridescent green sheen, or something just doesn't look right - throw it out. I hope this helps give you some measure of confidence and helps you save some money by not throwing out good food just because of some date on a package.

Wednesday, December 3, 2008

Exercise & Eating

As we are often reminded, our country is fighting the battle of the bulge. It should be no surprise that researchers are conducting studies on the effects of how, when & what we eat. There is a related series of studies that really caught my attention - they involved post-exercise eating. These three related studies measured insulin responses to varying carbohydrate-containing meals consumed after a workout and the results were interesting. If you are an athlete in training, none of this applies to you, but for the rest of us I think it is good to know. So what exactly did they study?

In the first study, participants exercised to burn 500 calories per day for 6 days and were given either a high carb drink or nothing immediately after exercise. The group that drank nothing had a 40% increase in insulin efficiency, while those who had the high carb drink showed no benefit. Wow! 40% you say - uh, what does that mean?

Science Lesson: Low intensity/endurance exercise creates ATP (adenosine triphosphate) via oxidation of triglycerides, while moderate to high intensity exercise creates ATP via metabolism of glycogen. Insulin efficiency is more likely to increase during metabolism of glycogen. The muscle contractions act like insulin during exercise, promoting the transport of glucose from the blood to the muscle cells. Exercise training increases glucose tolerance by increasing sensitivity to insulin, which can be measured by looking at lowered blood sugar levels. Which means even though your muscles need more glucose during exercise, your body needs less insulin to supply it.

The study results intrigued the scientists so the next study had two groups exercise for 75 minutes and then fed one group a meal of balanced carbs (intake = expenditure) and the other a 100 gram deficit of carbs; both meals were equal in calories. The group fed the low-carb meal had a better insulin response than the balanced-carb group. In the final study, the researchers wanted to know if the timing of the calorie intake mattered. The participants were given identical meals either before, immediately after or three hours after exercising for 75 minutes. There was no difference among any of the groups in their insulin responses.

So, at least from these early results, it appears that it is best not to eat, or at least eat something low in carbs, after exercising to get the most benefit from your workout. Darn, I guess no more doughnuts on Saturday mornings after my Pilates class! :)