In an enzyme-catalyzed reaction, the reaction rate initially increases as the substrate concentration is increased but then begins to level off, so that the increase in reaction rate becomes less and less as the substrate concentration increases.

A One-to-One Relationship In most biological environments, the concentration of enzymes is lower than the concentration of substrates. As long as this is true, the relationship between enzyme concentration and enzyme activity is directly proportional.

If the concentration of the substrate is low, increasing its concentration will increase the rate of the reaction. An increase in the amount of enzyme will increase the rate of the reaction (provided sufficient substrate is present).

For many enzyme molecules, their synthesis may be decreased with age; however, their turnovers are also lowered, so that apparent enzyme unit numbers, and thus their activities, can be maintained marginally at young levels even in old age.

In general, activity of various enzymes is lower in very old individuals than in the period of adulthood [1].

12 steps to better digestion as you age

1. Chew your food properly. Digestion begins in the mouth, with an enzyme in the saliva called amylase.
2. Maintain your smile.
3. Eat smaller meals.
4. Keep fluid intake up.
5. Keep moving.
6. Be mindful of lactose.
7. Speak to your doctor about medication.
8. Support stomach acid.

From Fuel to Stool: 5 Tips to Speed Up Digestion

1. Exercise for 30 minutes a day. Food and digested material is moved through the body by a series of muscle contractions.
2. Eat more fiber.
3. Eat yogurt.
4. Eat less meat.
5. Drink more water.

Here are six of the most common gastrointestinal problems — and what can be done about them.

1. Gastroesophageal Reflux Disease (GERD) Heartburn happens, but if it occurs regularly, you may need to be evaluated for GERD.
2. Chronic Diarrhea.
3. Chronic Constipation.
4. Gastroenteritis.
5. Ulcers.
6. Hemorrhoids.