Jones AO, Jacobs RM, Fry BE Jr, Jones JW, Gould JH
Am J Clin Nutr 1980 Dec;33(12):2545-2550

Eight commercially available partially digested gelatin liquid products that have been used as a source of protein in dietary regimens for weight reduction and for protein supplementation were analyzed for their elemental composition. These products were prepared either by dry ashing or wet digestion techniques that were suitable for the analysis of individual elements by their respective analytical methods. Analytical methods used to assess the elemental content included inductively coupled argon plasma emission spectrometry for Ca, Mg, P, Fe, Zn, Cu, Mn, Ni, Mo, V, Be, Co, Cr, Tl, Al, Te, Sn and Sb; atomic absorption spectrophotometry for Na and K; hybride generation with atomic absorption spectrophotometry for Se and As; anodic stripping voltammetry for Cd and Pb; and ion selective electrode for F. The content of almost all of the elements in these products was extremely low compared with the amounts supplied daily for normal individuals by usual sources of dietary protein, the adult United States Recommended Daily Allowances, and typical intakes from the Total Diet Study. The following elements were not detectable in significant amounts in these products by inductively coupled argon plasma emission spectrometry: Mo, V, Be, Co, Cr, Tl, Al, Te, Sn, and Sb. The results suggest that use of these predigested liquid protein products as a sole source of nutriment will result in an inadequate intake of all of the essential elements. These products contained insignificant amounts of Ce and Pb, nonessential toxic elements.

Comments: The "liquid protein" diet drink was analyzed chemically. It was found to be deficient in Calcium, Magnesium, Iron, Zinc, Copper, Sodium, Potassium, and everything else you can think of.

Klevay LM, Viestenz KE
Am J Physiol 1981 Feb;240(2):H185-H189

According to a new hypothesis based on epidemiologic observations, iatrogenic maneuvers, natural occurrences, and animal experiments, absolute or relative deficiency of copper is of prime importance in the etiology of ischemic heart disease. Male weanling rats were made copper deficient with a purified diet containing 0.79 microgram Cu/g diet and containing all other nutrients known to be essential. Deficiency was verified by a 39% increase in cholesterolemia. Electrocardiograms of copper-deficient rats showed several abnormalities including S-T segment depression for one-third to one-half of the R-R interval, bundle branch block with R waves three times normal height and width, Q waves, and second- and third-degree heart block. Copper deficiency shortened the lives of the rats by 73%. Copper deficiency is the only nutritional insult that has produced rapid unfavorable alterations in lipid metabolism, cardiac and arterial anatomy, and cardiac electrophysiology. Copper metabolism may be important in the etiology of ischemic heart disease and in the arrhythmias associated with the consumption of liquid-protein diets.

Comments: A diet which was deficient in copper was tested on rats. They all developed cardiac problems. It was theorized that the copper deficiency in the diet drink may have caused the heart attacks.

Amatruda JM, Biddle TL, Patton ML, Lockwood DH
Am J Med 1983 Jun;74(6):1016-1022

We have previously demonstrated that a hypocaloric, nutritionally deficient, liquid protein diet is associated with potentially life-threatening cardiac arrhythmias, which increased in frequency and complexity over the duration of the study. The present investigation was designed to evaluate the metabolic and cardiac changes associated with a hypocaloric, but otherwise nutritionally complete, diet. Six healthy, obese females from 154 to 182 percent of ideal body weight were evaluated in a metabolic ward for 48 days. The subjects ingested a weight maintenance diet during an eight-day period, which was followed by 40 days of an experimental diet containing 472 kcal of a mixture of protein (60 percent of calories), carbohydrate (25 percent), and fat (15 percent). This diet equaled or exceeded the recommended daily allowances for minerals, trace elements, vitamins, and essential fatty acids. The subjects were monitored for balances of nitrogen and minerals, as well as for the appearance of cardiac arrhythmias by 24-hour electrocardiographic recordings. Nitrogen balance was positive, and the previously demonstrated negative balances for potassium, sodium, calcium, magnesium, and phosphorus were either reversed or markedly decreased. In contrast to our previous study, no arrhythmias were observed in subjects ingesting the present experimental diet, and no significant change in cardiac rhythm was found in 13 obese, but otherwise healthy, outpatients. The data, based on a limited number of subjects, suggest that a hypocaloric diet vigorously supplemented with essential elements, micronutrients, and vitamins appears to be safer than the once popular, incomplete liquid protein preparation.

Comments: These researchers wanted to know: what happens when you give people a "liquid protein" diet that isn't lacking in minerals? So they got 19 volunteers, and fed them a diet that was mostly protein, but unlike that diet drink, it contained all the necessary vitamins and minerals. These 19 patients had no problems with their hearts.