The purpose of the present review is to describe how human physiology at very low carbohydrate intakes relates to the criteria for nutritional essentiality. Although we did not limit ourselves to one particular type or function of carbohydrates, we did primarily focus on glucose utilisation as that function was used to determine the recommended daily allowance. In the general population, the human body is able to endogenously synthesise carbohydrates, and does not show signs of deficiency in the absence of dietary carbohydrates. However, in certain genetic defects, such as glycogen storage disease type I, absence of dietary carbohydrates causes abnormalities that are resolved with dietary supplementation of carbohydrates. Therefore, dietary carbohydrates may be defined as conditionally essential nutrients because they are nutrients that are not required in the diet for the general population but are required for specific subpopulations. Ketosis may be considered a physiological normal state due to its occurrence in infants in addition to at very low carbohydrate intakes. Although sources of dietary carbohydrates can provide beneficial micronutrients, no signs of micronutrient deficiencies have been reported in clinical trials of low-carbohydrate ketogenic diets. Nonetheless, more research is needed on how micronutrient requirements can change depending on the dietary and metabolic context. More research is also needed on the role of dietary fibre during a low-carbohydrate ketogenic diet as the beneficial effects of dietary fibre were determined on a standard diet and several studies have shown beneficial effects of decreasing non-digestible carbohydrates.

Laparoscopic Roux-en-Y gastric bypass (RYGB) is considered the ‘gold standard’ for surgical treatment of morbid obesity. It is hypothesised that reducing the length of the common limb positively affects the magnitude and preservation of weight loss but may also impose a risk of malnutrition. The aim of this study was to compare patients’ nutrient and vitamin deficiencies in standard RYGB with a very long Roux limb RYGB (VLRL-RYGB). This study was part of the multicentre randomised controlled trial (Dutch Common Channel Trial), including 444 patients undergoing an RYGB or a VLRL-RYGB. Laboratory results, use of multivitamin supplements and reoperations were collected at baseline and 1 year postoperative. Primary outcome measure was nutrient deficiency after 1 year postoperative. Secondary outcome measure was the reoperation rate due to malabsorption. In total, 227 patients underwent RYGB and 196 patients underwent VLRL-RYGB. Most common deficiencies at 1 year postoperative were ferritin (17·2–18·2 %), Fe (23·4–35·6 %), K (7·4–15·2 %), vitamin B12 (9·0–9·9 %) and vitamin D (22·7–34·5 %). Patients undergoing VLRL-RYGB had slightly but significantly lower levels of Ca, Fe and vitamin D compared with those undergoing RYGB at 1 year postoperative, but significantly higher levels of folic acid and Na. Reoperation rates due to malabsorption were not significantly different between RYGB (2/227, 0·9 %) and VLRL-RYGB (7/196, 3·6 %) (P = 0·088). We concluded that patients undergoing VLRL-RYGB had significantly lower levels of Ca, Fe and vitamin D compared with those undergoing RYGB at 1 year postoperative, but higher levels of folic acid and Na. Reoperation rates did not differ. Close monitoring on nutrient deficiencies should be performed in patients undergoing VLRL-RYGB.

Field days on diagnosis of plant problems were conducted by Extension specialists at Michigan State University. The objective was to expose participants to a variety of plant growth problems. Techniques were developed to simulate crop injury from herbicide and fertilizer misapplication and environmental stress. Twenty demonstration plots each were established for corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. A specific problem was demonstrated in each plot. Two field days were held in 1985. One field day was conducted for agribusiness personnel and the other for Extension field staff. Promotion of the field days was a cooperative effort among Michigan Cooperative Extension Service, Michigan Pesticide Association, and Michigan Plant Food Council. Resource people conducting tours of the plots and leading discussions of the problems included a weed scientist, a soil fertility specialist, and a crop production agronomist. An evaluation survey indicated that this event was useful in furthering the understanding of plant growth problems. Based on the survey responses, future plant problem diagnosis field days are being planned in Michigan.

Knowledge of Palmer amaranth biology and physiology is essential for the development of effective weed management systems. The aim of this study was to investigate the response of Palmer amaranth gender to nutrient deficiency and light stress. Differential gender responses were observed for all the growth, phenology, and photochemistry parameters measured. Female plants, for example, invested more in height, stem, and total dry weight, whereas male plants invested more in leaf area and leaf dry weight. The growth rate of females was higher than that of male Palmer amaranth plants, although both followed similar declining trends as the experimental period progressed. Initiation of flowering of female plants occurred 6 to 8 d earlier compared with male plants. Nitrogen and to a certain extent phosphorous were the most influential nutrients that affected measured parameters in both Palmer amaranth genders, particularly under high light intensity. Electron transport rate and chlorophyll content of female Palmer amaranth plants compared with male plants was lower at high light intensity in combination with nitrogen and phosphorous deficiencies. There is a potential to manipulate Palmer amaranth population structure by altering microenvironments at the field level.

Up to one billion people live in areas where they may be at risk from I deficiency. Many of the debilitating effects of the deficiency may be irreversible, consequently it is essential to understand the mechanisms whereby lack of I can cause disease through decreased thyroxine and 3, 3',5-triiodothyronine (T3) synthesis. Since Se has an essential role in thyroid hormone metabolism, it has the potential to play a major part in the outcome of I deficiency. These effects of Se derive from two aspects of its biological function. First, three Se-containing deiodinases regulate the synthesis and degradation of the biologically active thyroid hormone, T3. Second, selenoperoxidases and possibly thioredoxin reductase (EC 1.6.4.5) protect the thyroid gland from H2O2 produced during the synthesis of thyroid hormones. The mechanisms whereby Se deficiency exacerbates the hypothyroidism due to I deficiency have been elucidated in animals. In contrast to these adverse effects, concurrent Se deficiency may also cause changes in deiodinase activities which can protect the brain from low T3 concentrations in I deficiency. Animals with Se and I deficiency have changes in serum thyroid hormone concentrations that are similar to those observed in patients with I deficiency disease. However such animal models show no thyroid involution, a feature which is characteristic of myxoedematous cretinism in man. These observations imply that if Se deficiency is involved in the outcome of I deficiency in human populations it is likely that other interacting factors such as goitrogens are also implicated. Nevertheless the protection of the thyroid gland from H2O2 and the regulation of tissue T3 levels are the functions of Se that are most likely to underlie the interactions of Se and I.

Birch (Betula pendula Roth) seedlings were grown under enhanced u.v.-B radiation and simulated forest-soil conditions, after which individual secondary metabolites were determined in the leaves. It was found that not all of the u.v.-absorbing secondary metabolites of the seedlings responded to supplementary u.v.-B radiation. Under increased u.v.-B radiation, significant increases in concentration were observed only for the major flavonoid, quercitrin, the minor flavonoid, myricetin-3-galactoside, and for chlorogenic acid. On the other hand, 3,4′dihydroxypropiophenone-3-β-D-glucopyranoside decreased under u.v.-B irradiation. The concentration of phenolic compounds in the leaves changed during the growing season (between two harvests) but this change was not related to u.v.-B enhancement. A low availability of mineral nutrients did not impair the capacity of the seedlings to accumulate u.v.-protecting phenolic compounds under increased u.v.-B radiation. The growth conditions used might have affected the intracellular concentrations of secondary metabolites, and thus furnished the birch seedlings with an increased tolerance of u.v.-B radiation. These findings point to the significance of certain phenolic components in the protection of deciduous trees against u.v.-B radiation.