The effect of caffeine on the exercise responses of six women habituated to caffeine (greater than 600 mg/day) was examined during 1-h running at 75% VO2 max on a motorized treadmill. Each subject completed a placebo (PL) and a caffeine ingestion (CC) trial while maintaining normal caffeine intake. The subject then abstained from caffeine for 4 days and again ran after receiving caffeine (CW). Caffeine dosage for all trials was 5 mg/kg body weight. Ingestion of caffeine after withdrawal (CW) resulted in the greatest physiologic effects. Exercise oxygen uptake was significantly elevated by 0.17 l/min over the PL and CC trials (P less than 0.05). The CW trials resulted in an overall R value of 0.79 +/- 0.04 compared with 0.85 +/- 0.08 for the PL and 0.83 +/- 0.04 for the CC trials. Caffeine had its greatest effect on the resting free fatty acid levels after withdrawal: 1104 +/- 425 mu Eq/l compared with 543 +/- 288 for the PL and 839 +/- 526 for the CC. Postexercise lactates were similar for all trials. Post-exercise plasma norepinephrine and dopamine were the highest after the CW trials. The results suggest that habitually high caffeine users acquire a tolerance to caffeine which reduces its effects during prolonged exercise. Furthermore, to magnify the effect of caffeine, habitual users should withdraw from caffeine use for about 4 days.
Different dietary proteins exert different effects on plasma cholesterol concentrations. Animal studies have shown that animal proteins, most notably casein, increase plasma total cholesterol concentrations compared with vegetable proteins, such as soy. Soy protein has been shown to be hypocholesterolemic in rats, swine, primates, and rabbits. Epidemiologic studies have disclosed that vegetarians have lower mean plasma cholesterol concentrations than populations consuming diets of mixed proteins, but it is unclear whether this effect results specifically from the animal or vegetable nature of the protein. In human clinical experiments, substituting soy protein for mixed protein reduces plasma total cholesterol concentration in hypercholesterolemic subjects, but it causes only a small, nonsignificant change in persons with normal plasma cholesterol concentrations. The mechanism responsible for the effects of different proteins on plasma cholesterol concentrations has not been established. One hypothesis suggests that animal proteins, which have a greater content of phosphorylated amino acids than vegetable proteins, interfere with bile acid reabsorption. Another hypothesis suggests that the amino acid content of the protein affects cholesterol absorption, tissue storage, synthesis, and excretion. The dietary protein may also alter cholesterol metabolism by affecting plasma hormone concentrations, either postprandially or over weeks to months. Among the hormones thought to be affected by dietary protein source are insulin, glucagon, and thyroid hormones. Gastrointestinal hormones, such as gastrointestinal inhibitory polypeptide, may also be affected by dietary protein.
Compliance with food safety recommendations was assessed among 357 university undergraduates, 112 males (31%) and 245 females (69%), in the context of the health belief model. Concerning meats, 87% of the students complied with purchasing, 75% with storage, and 42% with preparation recommendations often/always. Compliance was high with recommended purchasing (96%) and storage (99%) practices for raw eggs, but only 55% of students prepared eggs safely. Overall, the health belief model was a poor predictor of compliance with food‐safety recommendations. Findings suggest that college students would benefit from interventions focusing on the causes of microbial food contamination and those that assist them in overcoming perceived barriers to adopting safe food‐handling practices. Also, validated instruments are needed to help family and consumer sciences educators identify college students who are noncompliant with food‐safety recommendations.
Young male pigs were used to examine effects of dietary protein and fat sources on plasma cholesterol parameters. Diets providing 16 and 42% of metabolizable energy from protein and fat, respectively, were fed for 12-14 weeks. Protein was derived either from plant sources (50% from soybean meal and 25% each from corn and wheat) or from animal sources (90% from casein and 10% from lactalbumin). The polyunsaturated to saturated fat ratio in the diets averaged 3.0 in the polyunsaturated fat diets and 0.3 in the saturated fat diets. Cholesterol content of the four experimental diets (plant protein-polyunsatured fat; plant protein-saturated fat; animal protein-polyunsaturated fat; and animal protein-saturated fat) was 0.6 mg/kcal. Consumption of diets containing plant protein rather than animal protein reduced total plasma cholesterol levels by 50 mg/dl; high density lipoprotein (HDL) cholesterol levels were also lowered in pigs fed plant protein. Similarly, plasma cholesterol levels were approximately 40 mg/dl lower in pigs fed the polyunsaturated fat diets than in pigs fed the saturated fat diets. HDL cholesterol levels, however, were unaffected by source of fat fed. These results show that the hypocholesterolemic action of the plant proteins was as great as the hypocholesterolemic action of polyunsaturated fat and that consumption of plant proteins rather than animal proteins resulted in lower plasma cholesterol levels regardless of whether polyunsaturated or saturated fats were fed.
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