Purines and foods rich in purines

The Purines

Purines are a group of nitrogenous organic substances present in all living cells. The best known purines, as nitrogen bases of DNA and RNA, are adenine and guanine; these substances share with the other exponents of the family a molecular structure with two heterocyclic condensed nitrogen rings (since they derive from purine, where a penta-atomic ring condensed with an hexa-atomic ring is recognized). Among the other most significant purines we mention caffeine, theobromine and uric acid.

Excess Purine

The human organism continuously synthesizes the purines necessary for the synthesis of new nucleic acids; to this endogenous biosynthesis, which occurs mainly at the hepatic level, is added the dietary intake; moreover, there are ways of recovery, interconversion (formation of a purine from another) and degradation of excess purines.

Uric acid or urate is the main catabolite deriving from the degradation of purines.

Alterations of the Purine Metabolism and Hyperuricemia

In some subjects there are congenital deficiencies of enzymes involved in the interconversion, recovery and degradation pathways of purines. These and other changes in purine metabolism and uric acid excretion can cause hyperuricemia (excess uric acid in the blood) or hypouricemia (lack of uric acid in the blood).

Hyperuricemia is a fairly common condition characterized by an excess of uric acid in the blood. Hyperuricemia can trigger an arthritic condition called gout, characterized by an increase in uric acid in biological fluids; this excess leads to the formation and precipitation of uric acid crystals inside the joints, triggering gouty attacks (severe painful joint inflammation, with local redness and swelling). In addition to the joints, the most common areas of excess uric acid deposition are the kidneys (up to kidney failure) and the skin of the ears, hands and elbows (where the so-called tophi are formed, palpable masses visible under the skin).

Many of the subjects with hyperuricemia have a hereditary tendency to produce large amounts of uric acid, while it is rare for gout to be caused solely by the consumption of purine-rich foods in the absence of genetic predisposition. The fact remains that in the case of gout and hyperuricemia it is still important:

• limiting the consumption of foods rich in purines;
• following a sober diet (once gout was defined as the "disease of the rich" as it is typically associated with overeating);
• drink plenty of fluids, at least 2/3 liters a day, especially if it is hot (dehydration raises the risk of gouty attacks); water in abundance can prevent kidney stones to which the gouty ones are particularly exposed; herbal infusions can be a good solution to increase the consumption of liquids; moreover, some diuretic teas can favor the excretion of excess uric acid;
• try to reduce body weight, if in excess, while avoiding excessively restrictive diets; overweight people, especially those with concentrated abdominal fat, are more exposed to gout risk;
• limit or eliminate alcohol consumption; beer is particularly inadvisable because it has a high purine content compared to wine and other spirits;
• avoid fructose as a sweetener, as it increases uric acid retention;
• prefer sources of complex carbohydrates and reduce foods rich in fat;
• attention also to aspirin, which limits the filtration of uric acid to the kidney level; better to prefer paracetamol.

Foods rich in purines

• Foods that tend to trigger gout the most contain 150 to 1, 000 milligrams of purines every 100 grams. They include high-protein animal products such as anchovies, brains, consommé, meat sauce, herring, offal, meat extracts, minced meat, mussels and sardines.
• Other foods that can contribute to gout contain a limited amount of purines (50 to 150 milligrams per 100 grams). In severe cases it is necessary to limit these foods to no more than one portion per day; this class of food includes asparagus, dried beans, cauliflower, lentils, mushrooms, flour, oats, dried peas, oysters, spinach, cereals, fish, meat and poultry. Limit them to 90 grams five times a week.