Starches, Sugars and Obesity
Examples of monosaccharides are glucose, fructose, and glyceraldehyde. However, some . The difference being that the lone pair being donated is coming from the substituent at C .. Trehalose has the added advantage of being an antioxidant. Starch is processed to produce many of the sugars in processed foods. If you have a lollipop, you're eating simple carbs. But you'll also find simple sugars in more nutritious foods, such as fruit and milk. It's healthier to get your simple. The term “starches” in this review addresses only the starch polysaccharides . Much interest has been focused on the relationship between glycemic index and . In this sense, slowly digestible starch seem to be related to some benefits on.
Leptin is also produced by the stomach in response to feeding, being also involved in the acute regulation of food intake acting as a satiating hormone [ 75 ]. Ghrelin is a hormone with antagonistic effects to those of leptin.
It is known that ghrelin stimulates food intake and rises preprandially, initiating voluntary meals [ 76 ]. Recently, a study carried out in animals showed that diet composition influenced leptin and ghrelin production and secretion differentially.
Thus, carbohydrate feeding resulted in lower ghrelin and higher leptin levels than fat feeding [ 77 ]. In a recent review [ 24 ] authors discuss the relationship between GI, leptin and ghrelin. Insulin and insulin-mediated glucose uptake and metabolism in adipose tissue affect blood leptin concentration and its diurnal pattern.
The circulating ghrelin level is suppressed by carbohydrate-rich meals, presumably via glycemia and insulinemia. However, insulin-mediated leptin stimulation and ghrelin suppression per se are not consistent among studies. Thus, authors were not able to identify a clear relationship among GI, satiety-inducing leptin, and appetite-inducing ghrelin [ 24 ].
The GLP-1 and glucose responses after the standardized breakfast were inversely related. Animal studies suggest that this effect may be mediated by bacterial colonic fermentation and formation of SCFA. Thus, low-GI whole grain foods appear to be capable of improving glycemic and satiety control not only acutely, but also at a meal 10 h later.
A crossover study evaluated the effect of glucose and two starchy foods, varying in their content of rapidly and slowly available glucose, on plasma concentrations of GIP and GLP-1 in seven healthy volunteers BMI Each volunteer was studied on three occasions at least one week apart. In vitro characteristics were measured with the Englyst method, classifying the glucose fraction into rapidly available glucose RAG or slowly available glucose SAG to reflect the likely rate of release and absorption of glucose.
- Monosaccharides & Polysaccharides
- Starches, Sugars and Obesity
- Principles of Biochemistry/The Carbohydrates: Monosaccharides, Disaccharides and Polysaccharides
After the test meal was ingested, blood samples were taken at frequent intervals for 8 h. The intake of UCCS induced a sustained elevation of the incretin hormone of glucagon-like peptide-1 in the later stage — minwhich can decrease gastric emptying and improve glycemic response [ 79 ], as well as prolong satiety [ 80 ].
Simple vs Complex Carbs
More recently, a crossover study by Tarini and Wolever [ 57 ] evaluated the effect of fermentable fiber on gut hormone responses in healthy subjects. Four hours after the test drink a standard lunch was served.
Inulin significantly increased plasma glucagon-like peptide-1 concentrations at 30 min, and reduced ghrelin at 4. These results support the hypothesis that dietary fermentable fiber increases the production of colonic short-chain fatty acids, which may reduce postprandial free fatty acid concentration and favorably affects the release of gut hormones that regulate food intake [ 57 ].
All these properties make RS and SDS attractive dietary targets for the development of weight maintenance diets and diets for the prevention and treatment of metabolic syndrome and cardiovascular risk factors. Sugars, Obesity and Factors of the Metabolic Syndrome The three macronutrients have different effects on satiety, with protein being the most and fat the least satiating.
This hierarchy of macronutrients is also present in their thermic effect, where protein elicits the highest and fat the lowest thermic response after isocaloric ingestion [ 82 ]. Also, a diet combining a high protein and carbohydrate content results in a greater 24 h energy expenditure compared to a diet high in fat [ 83 ].
The macronutrient composition of the diet also affects the risk for cardiovascular disease. Thus, when in an ad libitum diet dietary macronutrient composition is varied, this can result in changes in body weight and cardiometabolic risk.
What are Polysaccharides?
As suggested before, different types of carbohydrates may also play a role. In the previous section, differences between types of starches have been discussed. Here we will discuss whether variations in the sugars content and type of sugars in the diet also play a role. Sugars, as part of the carbohydrates, are an important part of our diet.
Intake of Sugars, Appetite, Energy Expenditure and Body Weight Because different types of mono- and disaccharides have been shown to exert different effects on hunger and satiety, energy intake and energy expenditure, they may also exert different body weight effects. Therefore, modifying these types of sugars in the diet may sustain better weight management. Sugars, Appetite and Energy Intake Given the different physiological effects of sugars Figure 1one could assume that they also have a different effect on appetite and satiety.
Moran concluded that differences in food intake after different preloads are more related to the timing of ingestion relative to a test meal situation, whether the sugars are administered as pure sugars or as components of a dietary preload, and the overall volume of the preload than to intrinsic differences among the sugars.
Moreover, the practical relevance of the results from preload studies with fructose intakes higher than normal is questionable [ 88 ]. They conclude that there is no convincing evidence that such amount of fructose intake compared to sucrose or glucose is associated with an increase in food intake. There are only a few studies that have examined the effects of other sugars on appetite.
A study by Bowen et al. Acute appetite and energy intake was lower after consumption of lactose compared with glucose, which was consistent with differences in plasma ghrelin. Artificial sweeteners are widely used in diet products because they are sweeter than natural sweeteners but lack the calories. Yang reviewed epidemiological and intervention studies and concluded that artificial sweeteners do not account for more weight loss compared to natural sweeteners.
In some studies diet soda consumption was even associated with weight gain. Based on additional evidence from experimental studies, Yang suggests that the reason for these findings could be that artificial sweeteners do not activate food reward pathways in the same fashion as natural sweeteners. In artificial sweeteners there is a lack of calories after the sweet taste, which may result in compensatory overeating [ 91 ].
In conclusion, there is no consistent evidence that there is a difference in satiety and food intake after consumption of equal amounts of different sugars, either for the short- or long-term. On the other hand, artificial sweeteners increase appetite and the desire to eat compared to natural sweeteners, which makes their relevance for weight-loss purposes questionable. Effect on Appetite and Energy Intake It has been hypothesized that solid carbohydrates suppress subjective appetite and short-term food intake more than a carbohydrate in dissolved form [ 92 ].
They found that the postprandial area under the curve of appetite was not different between the solid and dissolved forms of sugars nor was food intake from an ad libitum pizza lunch one hour later. Sugars and Energy Expenditure Given the different metabolic pathways of sugars, different sugars may also have different effects on energy expenditure. Fructose increased EE significantly more than glucose.
Schwarz and colleagues [ 95 ] found a similar difference after comparing intravenous fructose and glucose administration. Brundin and Wahren [ 96 ] confirmed these findings. Sharief and Macdonald [ 97 ] compared the effects of glucose with galactose, lactose, maltose, sucrose, a glucose-galactose mixture and a glucose-fructose mixture, on EE.
Only sucrose and the glucose-fructose mixture showed a significant increase in EE compared to glucose [ 97 ]. Blaak and Saris [ 98 ] compared the thermogenic response to 75 g naturally enriched fructose, glucose, cane sugar, and digestible corn starch all mixed with mL water.
The energy expenditure was higher after fructose and sucrose than after glucose and starch [ 98 ]. Thus, the more pronounced increase in EE after sucrose or glucose-fructose mixture ingestion is due to the fructose component. The EE increasing effect of fructose is probably due to the energy cost of fructose metabolism to glucose in the liver and continued gluconeogenesis [ 95 ].
With respect to the effect of sugars on EE it can be concluded that only fructose or mixtures containing fructose significantly increase EE compared to other sugars.
Sugars, Body Weight and Body Composition Three reviews concerning this topic have been published recently. In the first review by van Baak and Astrup [ 37 ], the authors conclude that observational studies show fairly consistent inverse associations between the carbohydrate content and content of sugars in the diet and body weight and adiposity measures. This is supported by a limited number of randomized controlled trials RCTs that consistently show lower body weight when fat in the diet is replaced by carbohydrates, whether in the form of sugars or as starches.
In the second review, Ruxton et al. The third review by Dolan et al. The study sample was divided into three groups. Both Groups 1 and 2 were successful in reducing energy intakes and the percentage energy from fat in their diet. Group 1 was also successful in reducing percentage energy from sucrose at three months. These dietary changes resulted in significant reductions in body weight, percentage body fat and the waist-to-hip ratio in both groups, but there was no significant difference in weight-loss between Group 1 and 2.
In their review on sugars and body weight, van Baak and Astrup [ 37 ] concluded that a limited number of randomized controlled trials supported the positive association between BMI and SSB consumption that is found in observational studies, although not consistently [ 39 ].
A number of additional reviews on this topic has been published in the last two years [ 37, ]. InGibson [ ] published a systematic review on 23 cross-sectional, 17 prospective and four intervention studies in adults and children, as well as six reviews, using BMI, weight gain or adiposity as endpoints.
There were five randomized clinical trials; the two that involved adolescents indicated that efforts to reduce sugar-sweetened soft drinks slowed weight gain.
In adults, three small experimental studies also suggested that consumption of sugar-sweetened soft drinks caused weight gain. None of these trials in adults however was longer than 10 weeks and they all had a rather small study population. Saccharides are better known as carbohydrates literally hydrates of carbon. Relatively complex carboyhydrates are known as polysaccharides. The simplest carbohydrates are monosaccharides, which are small straight-chain aldehydes and ketones with many hydroxyl groups added, usually one on each carbon except the functional group.
Examples of monosaccharides include glucose dextrosefructose levulose and galactose. Monosaccharides are the building blocks of disaccharides such as sucrose and lactose and polysaccharides such as cellulose and starch. A disaccharide is formed when two monosaccharides simple sugars undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only.
Like monosaccharides, disaccharides are soluble in water. Three common monosaccharides are sucrose, lactose and maltose. An oligosaccharide is a saccharide polymer containing a small number typically three to nine of simple sugars monosaccharides. Oligosaccharides can have many functions; for example, they are commonly found on the plasma membrane of animal cells where they can play a role in cell-to-cell recognition. Polysaccharides are polymeric carbohydrate structures, formed of repeating units either mono- saccharides e.
Energy Availability and Storage While monosaccharides such as glucose provide short-term energy, polysaccharides provide longer storage of energy.
Cells use monosaccharides quickly. The molecules can bond to cell membrane lipids and aid in signaling. But for longer storage, monosaccharides must be converted to either disaccharides or polysaccharides via condensation polymerization. The polysaccharides become too large to cross a cell membrane, hence their storage capability.
Starches represent polysaccharides used by plants and their seeds to store energy. Starches are made of the glucose polymers, amylose and amylopectin. Polysaccharides can be broken down or hydrolyzed in the cell, as energy is needed in the form of monosaccharides. This is how animals use plant starches to make glucose for metabolism. The base monosaccharide of cellulose is glucose.
The straight cellulose molecules make up rows in a stable form via the weak but prevalent hydrogen bonds between them. Made by plants, fungi and algae, cellulose provides the rigid structure of plant cell walls, which also protect against diseases.
Many animals cannot digest cellulose, but those that can use intestinal micro-organisms and enzymes for the task.
Fermentation occurs in the colon of other animals and humans that cannot digest cellulose.