In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results: Weight Watchers makes healthy food more tempting to members by assigning zero SmartPoints to a list of over healthy foods. I have low thy Powered by WordPress v 3. Haylie Pomroys plan works for almost every person. Zero-point foods include eggs, skinless chicken, fish, beans, tofu and non-fat plain yogurt, among many other high-protein, low-calorie foods. The use of short-term fasting, or various forms of intermittent fasting have been used as a form of dieting to circumvent this issue.
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The first source to which the body turns is glycogen by glycogenolysis. It is created from the excess of ingested macronutrients , mainly carbohydrates. When glycogen is nearly depleted, the body begins lipolysis , the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells , are broken down into glycerol and fatty acids , which can be used to generate energy. Some weight loss groups aim to make money, others work as charities.
The former include Weight Watchers and Peertrainer. The latter include Overeaters Anonymous and groups run by local organizations. These organizations' customs and practices differ widely. Some groups are modelled on twelve-step programs , while others are quite informal.
Some groups advocate certain prepared foods or special menus, while others train dieters to make healthy choices from restaurant menus and while grocery-shopping and cooking. A study published in the American Journal of Preventive Medicine showed that dieters who kept a daily food diary or diet journal , lost twice as much weight as those who did not keep a food log, suggesting that if you record your eating, you would be more aware of what you eat and, therefore you wouldn't eat as many calories.
A review found that existing limited evidence suggested that encouraging water consumption and substituting energy-free beverages for energy-containing beverages i. References given in main article.
Fasting is when there is a long time interval between the meals. In dieting, fasting is not recommended, instead, having small portions of food after small intervals is encouraged. Lengthy fasting can also be dangerous due to the risk of malnutrition and should be carried out only under medical supervision. During prolonged fasting or very low calorie diets the reduction of blood glucose, the preferred energy source of the brain , causes the body to deplete its glycogen stores.
Once glycogen is depleted the body begins to fuel the brain using ketones, while also metabolizing body protein including but not limited to skeletal muscle to be used to synthesize sugars for use as energy by the rest of the body. Most experts believe that a prolonged fast can lead to muscle wasting, although some dispute this. The use of short-term fasting, or various forms of intermittent fasting have been used as a form of dieting to circumvent this issue.
While there are studies that show the health and medical benefits of weight loss, a study in of around Finns over an year period showed that weight loss from dieting can result in increased mortality, while those who maintained their weight fared the best. Many studies have focused on diets that reduce calories via a low-carbohydrate Atkins diet , Scarsdale diet , Zone diet diet versus a low-fat diet LEARN diet, Ornish diet.
The Nurses' Health Study , an observational cohort study , found that low carbohydrate diets based on vegetable sources of fat and protein are associated with less coronary heart disease. A long term study that monitored 43, Swedish women however suggests that a low carbohydrate-high protein diet, used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, is associated with increased risk of cardiovascular disease.
A meta-analysis of randomized controlled trials by the international Cochrane Collaboration in concluded  that fat-restricted diets are no better than calorie-restricted diets in achieving long term weight loss in overweight or obese people. A more recent meta-analysis that included randomized controlled trials published after the Cochrane review    found that low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year.
These results can be understood because weight loss is mainly governed by daily caloric deficit and not by the particular foods eaten. Additional randomized controlled trials found that:. The American Diabetes Association recommended a low carbohydrate diet to reduce weight for those with or at risk of Type 2 diabetes in its January Clinical Practice Recommendations. The diet based around this research is called the Low GI diet.
Low glycemic index foods, such as lentils, provide a slower, more consistent source of glucose to the bloodstream, thereby stimulating less insulin release than high glycemic index foods, such as white bread. The glycemic load is "the mathematical product of the glycemic index and the carbohydrate amount". In a randomized controlled trial that compared four diets that varied in carbohydrate amount and glycemic index found complicated results: Diets 2 and 3 lost the most weight and fat mass; however, low density lipoprotein fell in Diet 2 and rose in Diet 3.
Thus the authors concluded that the high-carbohydrate, low-glycemic index diet was the most favorable. A meta-analysis by the Cochrane Collaboration concluded that low glycemic index or low glycemic load diets led to more weight loss and better lipid profiles.
However , the Cochrane Collaboration grouped low glycemic index and low glycemic load diets together and did not try to separate the effects of the load versus the index. From Wikipedia, the free encyclopedia. Very low calorie diet. Weight loss effects of water. Medical research related to low-carbohydrate diets. Retrieved 29 November The American Journal of Clinical Nutrition. Retrieved 22 December Obesity Biographies of Disease.
Retrieved 17 December Retrieved 20 June Chalem 5 September Retrieved 26 December The Father of the Low-Carbohydrate Diet". Retrieved 28 December A Century of Panic and Pleasure. Lipids in Health and Disease.
Archived from the original on 27 December Retrieved 14 February Retrieved 26 July The Lifestyle Heart Trial". Gatekeepers of Life and Death". Retrieved 1 May Cochrane Database of Systematic Reviews 2: Retrieved 21 September Cochrane Database of Systematic Reviews.
American Journal of Clinical Nutrition. The Journal of Nutrition. Archives of Internal Medicine. Photomicrograph 50X of a cross section through the proventriculus showing folds of mucous membrane P ; deep proventricular glands GP ; capsule connective tissue around the glands arrow head ; muscle layer m ; serosa connective tissue with blood vessels S , and the lumen L From: Photomicrograph X of longitudinal section of the gizzard showing folds of mucous membrane lined by simple prismatic epithelium P ; simple tubular glands Gs in the lamina propria constituted by connective tissue Lp ; secretion of glands S that are continuous with the cuticle or koilin ; C , part of muscle layer m , interpersed with bundles of connective tissue Tc From: Photomicrograph X of the koilin of an Eclectus Parrot Eclectus roratus.
Note the regular, columnated structure of the koilin layer K and its association with the glandular epithelium E of the ventriculus From: De Voe et al. A, koilin, B, crypts, C, glands that secrete koilin, D, epithelial surface, E, desquamated epithelial cells, 2 Mucosa of the gizzard.
A, koilin, B, secretion in gland lumens and crypts, and 3 Koilin layer. A, secretion column, B, koilin-layer surface, C, horizontal stripe indicating a 'pause' in secretion of the koilin, D, cellular debris. Eglitis and Knouff Vultures of the seas -- Animals are primarily limited by their capacity to acquire food, yet digestive performance also conditions energy acquisition, and ultimately fitness. Optimal foraging theory predicts that organisms feeding on patchy resources should maximize their food loads within each patch, and should digest these loads quickly to minimize travelling costs between food patches.
GPS-tracking of 40 Wandering Albatrosses from the Crozet archipelago during the incubation phase confirmed foraging movements of between — km, giving the birds access to a variety of prey, including fishery wastes. Using miniaturized, autonomous data recorders placed in the stomach of three birds, the first-ever measurements of gastric pH and temperature in procellariformes were obtained.
Such low stomach pH gives Wandering Albatrosses a strategic advantage because it allows a rapid chemical breakdown of ingested food and rapid digestion. This is useful for feeding on patchy, natural prey, but also on fishery wastes, which might be an important additional food resource for Wandering Albatrosses. It is likely that this physiological characteristic evolved as a response to a diet largely composed of squid, and to a patchy distribution of this food resource resulting in large, infrequent meals.
The strategy of Wandering Albatrosses is to cover long distances rapidly and at low costs to increase the probability of encountering dispersed prey patches whose distribution is unpredictable. Knots with large gizzards consumed far more molluscs with shells than the birds with smaller gizzards.
Birds with smaller gizzards simply couldn't feed fast enough. By allowing them to crush more shell per gizzard-full, larger gizzards gave birds the edge. Thus, even though it is energetically costly for the knots to maintain a larger gizzard, when the bird needs to get the most out of its crunchy diet, it's a price worth paying. So, the birds' gizzards enlarge as they fatten for migration.
Because the molluscs' shells stay the same size as the molluscs shrink, the amount of shell a bird must process to eat its fill also increases.
But with their larger gizzards, the birds can still make the most of even the crunchiest winter diet! Within 14 days, they showed a doubling of the size of their gizzards. Red Knots have strong muscular gizzards for feeding on molluscs. A shift back to a mussel diet induced about a doubling in gizzard mass in just a few days. As the knots were fed progessively smaller mussels day 22 to day 46 that are easier to crush, gizzard mass again declined.
A switch back to a soft food pellet diet caused a further decline in gizzard mass. Finally, a switch back to a mussel diet again cause a rapid increase in gizzard mass From: Piersma and Drent Ostrich Struthio camelus stomach. Note how particle size of material in the gizzard ventriculus is smaller than in the proventriculus due to the grinding action of the muscular walls plus small pebbles gastroliths.
The capacity to reduce particle size is related to the metabolic demands of a species. Therefore, particle size reduction is often considered the key digestive difference between ecto- and endotherms that allows endotherms to rely on shorter digesta retention times without losing digestive efficiency, and hence facilitate the high level of food intake necessary to meet their increased metabolic requirements. In contrast, adaptations for chewing intrinsically increase the weight of the head.
The use of the gizzard system has the potential advantages that intake rate is not limited by chewing, that no investment in dental tissue is necessary, and that dental wear is not a determinant of senescence as observed in mammals.
The absence of age-dependent tooth wear might even be a contributing factor to the slower onset of senescence in birds as compared to mammals. On the other hand, the use of a gizzard requires the intake of suitable grit or stones—an action that represents, in the few studies where this has actually been quantified in birds, a relevant proportion of feeding time Fritz et al.
Gastrointestinal tracts of a carnivorous hawk, an omnivorous chicken, and 4 herbivorous birds. Note larger size of crop in omnivore and herbivores, and particularly in hoatzin. Ceca are small in hawks and relatively large in grouse. Although ceca are relatively small in Hoatzins , Emus, and Ostriches, an expanded foregut Hoatzins , a much longer midgut Emus , or a much longer colon Ostriches compensates for this From: Stevens and Hume Over-reliance on the passive pathway provides metabolic advantages and ecological constraints.
It does provide birds with an absorptive process that can deal with rapid and large changes in intestinal sugar concentrations.
The passive pathway is also energetically inexpensive to maintain and modulate. However, passive absorption through the paracellular pathway is dependent on concentration gradients. In the absence of a transport system that selects which materials to absorb, this non-discriminatory pathway may also increase vulnerability to toxins, and thus constrain foraging behavior and limit the breadth of the dietary niche of the birds.
Another problem is that when luminal sugar concentrations are lower than those in plasma, glucose may diffuse back into the lumen. Cross-section of the intestine ileum of a Spotted Tinamou Nothura maculosa. Villi are lined with columnar epithelium EP , including goblet cells arrows that secrete mucus. The muscle layer includes longitudinal fibers MI on the perimeter, circular fibers Mc , and additional longitudinal fibers at the base of the villi muscularis muscosae; MM From: Chikilian and de Speroni Blue-headed Parrots at clay lick.
Meyer-Rochow and Gal determined that the pressures involved could be approximated if they knew the 1 distance the feces traveled, 2 density and viscosity of the material, and 3 shape, aperture, and height of the anus above ground. How penguins choose the direction of defecation, and how wind direction factors into that decision, remain unknown.
Avian Pancreas tissue Source: The Avian Digestive Tract. Avian geophagy and soil characteristics in southeastern Peru.
Luminal morphology of the avian lower intestine: Histological aspects of the stomach proventriculus and gizzard of the Red-capped Cardinal Paroaria gularis gularis. Comparative study of the digestive system of three species of tinamou. Crypturellus tataupa, Nothoprocta cinerascens , and Nothura maculosa Aves: Journal of Morphology Journal of Experimental Zoology Rictal bristle function in Willow Flycatcher. Dysplastic koilin causing proventricular obstruction in an Eclectus Parrot Eclectus roratus.
Journal of Avian Medicine and Surgery Anatomy and physiology of the digestive system in fowl. Pages in Proc. An histological and histochemical analysis of the inner lining and glandular epithelium of the chicken gizzard. American Journal of Anatomy An ecomorphological study of the raptorial digital tendon locking mechanism.
Dietary and developmental regulation of intestinal sugar transport. Digesta retention patterns in geese Anser anser and turkeys Meleagris gallopavo and deduced function of avian caeca. Comparative Biochemistry and Physiology A Histological and global gene expression analysis of the 'lactating' pigeon crop. Vultures of the seas: Evolution of the structure and function of the vertebrate tongue. Journal of Anatomy Light and scanning electron microscopic study of the tongue in the cormorant Phalacrocorax carbo Phalacrocoracidae, Aves.
Functional morphology of the tongue in the nutcracker Nucifraga caryocatactes. A tropical horde of counterfeit predator eyes. Instructed learning in the auditory localization pathway of the Barn Owl. The morphology of the bill apparatus in the Steller's Sea Eagle. Wild Bird Society of Japan, Tokyo. Use of dung as a tool by burrowing owls. The integration of energy and nitrogen balance in the hummingbird Sephanoides sephaniodes. Does gut function limit hummingbird food intake?
Physiological and Biochemical Zoology Pressures produced when penguins pooh—calculations on avian defaecation. Scare tactics in a neotropical warbler: Gliding flight and soaring. Theoretical Ecology Series, vol. Modelling the flying bird C. Structure, form, and function of flight in engineering and the living world. Phenotypic flexibility and the evolution of organismal design.
Trends in Ecology and Evolution The hummingbird tongue is a fluid trap, not a capillary tube. Between air and water: Use of prey hotspots by an avian predator: Structure and mechanical behavior of a toucan beak. Movement and direction of movement of a simulated prey affect the success rate in Barn Owl Tyto alba attack. Musculoskeletal underpinnings to differences in killing behavior between North American accipiters Falconiformes: Accipitridae and falcons Falconidae.
Journal of Morphology, online early. Le Bohec, and Y. Adjustments of gastric pH, motility and temperature during long-term preservation of stomach contents in free-ranging incubating King Penguins.
Journal of Experimental Biology A tough nut to crack. Adaptations to seed cracking in finches. Cost-benefit analysis of mollusc-eating in a shorebird. Optimizing gizzard size in the face of seasonal demands. How do woodpeckers extract grubs with their tongues? Why do woodpeckers resist head impact injury: Functional morphology of raptor hindlimbs: The turning- and linear-maneuvering performance of birds: Canadian Journal of Zoology Hummingbird jaw bends to aid insect capture.
A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems. I - Introduction to Birds. VII - Circulatory System. Back to Avian Biology. Drawings of the digestive tracts of A a Greylag Goose and B a Wild Turkey and retention times of a solute, 2-mm particles, and 8-mm particles in the goose and turkey digestive systems Figure from Frei et al.
The closed, air-filled spaces reduce overall weight without loss of rigidity. The capillary ratchet mechanism Surface tension transport of prey by feeding shorebirds: The serrated leading-edge feather of an owl Norberg Vortex generators on an airplane wing.
Fish-eating species like cormorants below - typically have small, undifferentiated tongue because fish are often swallowed whole. Representative caterpillar false eyes and faces. In some, like woodpeckers, the 'sticky' saliva aids in capturing prey. In others, like swifts, saliva is used in nest building see photo below. The muscular walls of the esophagus produce wave-like contractions peristalsis that help propel food from the oral cavity to the stomach.
Anhinga swallowing a large fish. HCL and pepsinogen are secreted by the deep glands see photomicrograph below. Pepsinogen is converted into pepsin a proteolytic, or protein-digesting, enzyme by the HCl. The cuticle is secreted by simple tubular glands see photomicrograph below.
Grinding action may, particularly in seed-eating birds, be assisted by grit and stones deliberately ingested. The avian gastrointestinal tract, unlike that of mammals, executes distinct reverse peristaltic movements that are critical to optimal digestive function Duke The gastric reflux allows material in the gizzard to reenter the proventriculus for additional treatment with acid and pepsin. Villi are projections from the intestinal wall that increase the amount of surface area available for absorption.
Further increasing the surface area are the numerous microvilli of the cells lining the surface of the villi. Inside each villus are blood vessels that absorb nutrients for transport throughout the body. Caeca are histologically similar to the small and large intestines and found in a wide variety of birds. In these large ceca, food particles are acted upon by cecal secretions, bacteria, and fungi and nutrients can be absorbed.
Lymphoid ceca are not important in digestion but contain lymphocytes white blood cells that produce antibodies Clench At various times and under various conditions, ceca are the site for 1 fermentation and further digestion of food especially for the breakdown of cellulose and absorption of nutrients, 2 production of antibodies, and 3 the use and absorption of water and nitrogenous components Clench The bursa is most prominent in young birds and serves as the area where B-lymphocytes the white blood cells that produce antibodies are generated T-lymphocytes are generated in the Thymus.
Bile emulsifies fats or, in other words, breaks fats down into tiny particles. Emulsification is important because it physically breaks down fats into particles than can then be more easily digested by enzymes lipase produced by intestinal cells and the pancreas. This 'juice' contains a bicarbonate solution that helps neutralize the acids coming into the intestine from the stomach plus a variety of digestive enzymes.
The enzymes help break down fats, proteins, and carbohydrates. The pancreas also produces the hormones insulin and glucagon which regulate blood sugar levels cells that produce these two hormones make up the 'islets of Langerhans', one of which is represented by the light-colored, circular structure in the photomicrograph below. Hit 'Reload' or 'Refresh' to View Again!
Particle retention time hr. Flamingos use a series of projections, or lamellae, to filter tiny food items from debris in the water. Wrens use their thin, probing bill to capture small insects.
Curlews use their long bill to probe mudflats for small invertebrates. Finches do not simply bite the seeds; instead; the lower mandible is moved toward the tip of the bill in a slicing motion.
When most of the coat has been cracked or removed, the lower mandible is moved from side to side to remove the rest of the shell, thus releasing the kernel. Some large finches also have raised hard surfaces in the upper palate that function as anvils so large seeds can be held firmly while the lower mandible slices and cracks the sides of the seed. As tricky as nutcracking sounds, most birds accomplish it rapidly, shelling small seeds in a few seconds and large finches can crack open and devour a large seed or nut in less than twenty seconds.
Big mouths get hummingbirds an in-flight meal - Hummingbirds have bendy lower beaks to help them catch insects Yanega and Rubega The flexibility allows long-beaked birds to open their mouths wide enough to hunt on the wing. Hummingbirds use their long, narrow beaks to probe flowers for nectar, but they also need insects for essential nutrients. It wasn't clear how they could catch them; birds that hunt flying insects usually have short beaks to help them open their mouths wide.
Pilcher, Nature Science Update. The force produced by talons may be related to time of activity. Owls hunt when light levels are low so if an attacking owl misses its prey, relocating it may be difficult.
Hawks are diurnal hunters and can use visual cues during and after an attack. If unable to subdue prey initially, they can relocate prey visually and catch it. Given the morphological differences and hunting behaviors of these raptors, how well do those characteristics relate to prey-size selection?
Eastern Screech-Owls prey on insects, small birds, and small mammals. Red-tailed Hawks subsist primarily on rodents and larger mammals such as skunks and rabbits. Red-shouldered Hawks , like Barred Owls, subsist mainly on medium-sized mammals such as squirrels and chipmunks, but also prey on frogs and salamanders.
American Kestrels , like Eastern Screech-Owls, eat mostly insects and small mammals. Bristles occur most prominently around the eyes "eyelashes" , the lores, the nostrils, and around the rictus corners of the mouth. Not all birds have bristles. Rictal bristles are prominent in many insectivorous birds, particularly aerial insectivores like nightjars Order Caprimulgiformes and flycatchers Family Tyrannidae , and may be used as sensory organs to help locate and capture prey, much like mammals use whiskers.
In addition, bristles around the mouth may help protect the eyes from food items a bird is trying to capture Conover and Miller The photo to the right shows the rictal bristles of a Hooded Warbler.
Goose tongue -- The dorsal surface of the tongue of Middendorff's Bean Goose Anser fabalis middendorffii has an anterior region that extends for five-sixths of its length plus a posterior region. Large conical papillae indicated by arrowhead to the right are located in a row between the anterior and posterior regions.
On both sides of the anterior region, lingual papillae are compactly distributed, and small numbers of large conical papillae are found between the lingual papillae. The dorsal surface of the tongue is covered by numerous fine processes, which help hold food on the tongue's surface.
The taste buds of birds may be located in the upper beak epithelium, in the anterior mandible, and the mandibular epithelium posterior to the tongue. Some taste buds are also located ventrolaterally on the anterior tongue. Arrows show lingual hairs on the lateral sides. Lingual papillae arrows are compactly distributed on the tongue, and large conical papillae arrowhead are scattered among them.
Energy and nitrogen balance in a hummingbird -- Keeping fit and healthy on a low-fat, fiber-free diet isn't easy, but despite the nutritional disadvantages of life on a liquid lunch, hummingbirds flourish by supplementing their nectar intake with tiny arthropods.
But the beneficial snacks come at a high metabolic price; flies don't sit still, so hummingbirds work hard chasing their protein. Back in the lab, the team prepared nectar solutions with different concentrations of amino acids to see how much protein the birds needed to maintain a stable body weight.
By filming the birds as they sipped from feeders, they measured the amount of energy and nitrogen that the birds consumed. To calculate the bird's nitrogen uptake, they also needed to know how much waste nitrogen the birds lost. So, they collected all of the birds' feces, making sure that none dried out, and measured the nitrogen content. Not surprisingly, the birds that were fed small amounts of protein began losing weight quickly, even though they were able to sip as much high-energy nectar as they wanted.
However, the birds that were fed 1. What does that translate to in terms of flies? The birds that had a reduced nectar supply also maintained a stable weight, although they went into torpor overnight to conserve energy. But the birds fed flies alone began losing weight, no matter how hard they worked to feed themselves. She suspects that although the flies should supply all of the hummingbirds needs, the birds simply have to work too hard to catch flies to rely on them as their soul food source.
Flush—pursuit foragers use exaggerated and animated foraging movements to flush potential insect prey that are then pursued and captured in flight. The Myioborus redstarts comprise 12 species of flush—pursuit warblers found in montane forests of the American tropics and subtropics.