One of the most important resolutions you can make for weight loss is to stop thinking "low-fat" and start thinking "right kind of fat". At first glance, low fat diets seem to be a wise choice for weight loss. After all, ounce for ounce, fats have more than twice as many calories as carbohydrates and proteins. The problem is that food is much, much more than a source of calories. Dietary components, including fats, are biological response modifiers - they influence biological functions. The focus should not be on eating low-fat but on eating the right types of fat to optimize physiology that favors body fat reduction. 

There are many different types of fats, including oils, which are fats that are liquid at room temperature. To treat all fats as equal with regard to their role in weight loss is a costly mistake. Besides containing calories, fats affect body composition (muscle vs. fat) by influencing such things as: 

1. Speed of gastric emptying and food absorption

2. Composition and function of cellular membranes

3. Partitioning of nutrients between burning for energy and storage

4. Mitochondrial proton leakage (resting metabolic rate)

5. Production of hunger-modulating biochemicals

Dietary fats slow gastric emptying and absorption of food. These are beneficial effects for weight loss. Slower emptying of food from the stomach produces earlier satiety with the result being less food consumed. The body will burn more of its stored fat for energy if there is a slow steady supply of nutrients being absorbed from the intestinal tract. When fats are part of a meal, food empties more slowly from the stomach and is more gradually absorbed into the bloodstream. The best fatty acid for slowing gastric emptying and food absorption appears to be oleic acid, which is concentrated in olives, avocados, almonds, pistachios, sesame seeds, peanuts, pecans, cashews, hazelnuts, Brazil nuts, macadamia nuts, canola oil and high-oleic variety safflower oil. Beginning meals with some oleic acid-rich food is a good idea. For example, eat a salad with avocado or olive oil.

Cell membranes, the structures that encase cells and sub cellular organelles, are composed largely of fatty acids derived from the diet. Fatty acids can be classified as saturated, mono unsaturated or polyunsaturated. Compared with the other two groups of fats, saturated fats are more solid and produce stiffening and consequent impaired functioning of cell membranes. Foods high in saturated fat are beef, eggs, pork, lamb, and dairy products. I hate to be the bearer of bad news, but chocolate is one of the richest sources of saturated fat. Polyunsaturated fatty acids (PUFAs) are comprised of two families: omega 6 (largely found in vegetable oils) and omega 3 (found in cold-water fish). "Omega 6" and "3" simply has to do with the chemical structure of the fatty acid molecule. Omega 3 fatty acids have a lower melting point, making them more fluid than the omega 6s. This fluidity appears to confer healthful effects upon the functioning of cellular membranes. Omega 3s, like DHA, are associated with efficient insulin binding to cell membranes - an important thing for losing body fat. High levels of linoleic acid (found in vegetable oils) and low levels of DHA in muscle cell membranes have been associated with insulin resistance and obesity in adults. The importance of Omega 3s in preventing obesity begins very early in life. A study of children under two years of age found an association between higher DHA levels and lower fasting blood sugar levels (an indication of better insulin sensitivity). Children with higher DHA levels were those whom had been breast-fed. Mother's milk contains DHA but not all American infant formulas do. DHA sufficiency should be considered as early as in utero - the pregnant mother's diet should also be supplemented with a pure quality source of DHA. 

Different types of fats and oils have very different effects on the way the body burns energy and stores fat. Most of the work in this area has been done with animals but let's start with one small human study that measured resting metabolic rate and diet-induced thermogenesis (DIT) in response to varying the type of fat in the diet. Six male subjects followed a diet high in saturated fat for two weeks and during another two week period followed a diet high in PUFAs. Both diets contained the same amount of calories and the same contribution of fat, carbohydrate and protein (46%, 37% and 17%, respectively). Resting metabolic rate (the speed at which calories are burned to maintain bodily functions at rest) was found to be significantly higher after the subjects followed the high PUFA diet. This study also found the DIT to be higher in all subjects after consuming a breakfast high in PUFAs versus saturated fats. DIT refers to the increase in body heat production after a meal. DIT involves increased energy production (burning of calories), which is used in part to digest, absorb and metabolize the food. 

PUFAs are the best class of dietary fat for weight loss. The saturated and monounsaturated fats are more easily converted into body fat than are the PUFAs. What's more, PUFAs have the amazing effect of helping to orchestrate how food will be metabolized in the body. PUFAs shunt glucose into glycogen storage and steer fatty acids away from storage and toward oxidation (burning for energy). Again, the omega 3s appear to be the stars in this story. They inhibit the transcription of genes encoding for the fat-building enzyme, fatty acid synthase. Omega 3s increase the formation of enzymes that carry fatty acids into the mitochondria of the cells where food is oxidized to produce ATP (energy). They increase the rate of "burning" of fatty acids in the mitochondria and in other organelles called peroxisomes. Omega 3s produce a tremendous increase in the formation of uncoupling proteins. Uncoupling proteins are located in the mitochondria and have the effect of wasting energy. They raise the body's resting metabolic rate while producing heat. Omega 3s produce beneficial effects on hormones, including leptin, which reduces appetite and activity of fat-building enzymes, while increasing fat burning. Omega 3s alter the activity of enzymes involved in fat cell differentiation, resulting in fewer and smaller fat cells and less overall body fat. 

An impressive study with rats tested four different diets. Three diets contained 58% fats; saturated, omega 6, or omega 3. The fourth group was low fat (10%). It was found that the rats in the saturated fat group gained the most body fat, followed by the omega 6 and then the low fat groups. The omega 3 group gained the least fat. This study also found that the various groups of rats exhibited different levels of activity within the hypothalamus- the part of the brain involved with regulation of both food intake and energy expenditure. 

A study in humans also found different types of supplemental fatty acids to have differing effects on body fat mass. One group of subjects took six grams of fish oil for twelve weeks. The other group was given six grams of sunflower oil. Both groups of subjects continued to eat their normal diets. Whereas the sunflower oil-supplemented group experienced no weight loss, the group given fish oil did lose a significant amount of body fat.

It's clear that omega 3 fatty acid-rich foods are of paramount importance for weight loss. These include the cold-water fish, such as salmon, mackerel and sardines. The problem is that fish contain a fair amount of toxins. Eat lower on the food chain (smaller fish) to reduce toxin consumption. My recommendation for most healthy people (pregnant and nursing women excluded) is to eat ocean fish several times a week. Take vitamin C supplements to help the body rid the toxins. If you want to go an extra step, you can be tested for mercury toxicity by urine porphyrin analysis.

Increase your intake of EPA and DHA by taking fish oil capsules. Good processing of fish oil removes virtually all the toxins, although some brands are of questionable quality. One that is outstanding for purity and resistance to rancidity is EPA-DHA 720. Each capsule of EPA-DHA 720 contains a whopping 430 milligrams of EPA, probably the most important omega 3 for weight loss. EPA and DHA are also available in flavored liquid and chewable capsules for those who cannot swallow capsules. For vegans, I recommend algae-derived O-Mega-Zen3, which is in a vegicap. For maximal absorption, take fish oil supplements with a meal containing fats and/or oils. Individuals with suboptimal digestion and absorption need additional help, such as digestive enzymes.

Although EPA and DHA seem to be the most important omega 3 fatty acids for weight loss, another one called alpha linolenic acid should also be part of the diet. It is the first one we become deficient in with weight loss. Alpha-linolenic acid is found in greatest concentrations in hemp seeds, canola, walnuts, wheat germ, and especially flax seeds. I recommend using flax seed oil on salads. I like mixing it with balsamic vinegar and mustard or with garlic and lemon juice. The brands of flax seed oil I recommend, because of their high quality processing to assure freshness of this delicate oil, are Flora and Omega Nutrition. I prefer Flora because the oil is packaged in glass rather than plastic bottles. Keep flax seed oil refrigerated, use it within six weeks of opening the bottle or by the expiration date (whichever comes first), and never cook with it. When increasing your intake of omega 3 fatty acids, it's wise to take a vitamin E supplement to protect these unstable fats from free radical damage in the body. Also, add a supplement of a GLA (gamma linolenic acid)-rich oil, like borage oil, to avoid developing a deficiency (EPA slows the body's production of GLA).

Some oleic acid-rich foods should also be part of the regular diet. These include olives, avocados, almonds, pistachios, pecans, cashews, filberts, and macadamia nuts. Nuts are best eaten raw, with dry-roasted being second best. Avoid eating nuts that have been roasted in oils. Limit your intake of omega 6 fatty acid-rich oils (sunflower, corn, safflower, cottonseed, soybean). Whereas most people have to make a concerted effort to eat enough omega 3s, omega 6s are widely distributed in our food supply. It has been estimated that the average consumption of omega 6 oils increased from one kilogram per year in 1909 to 12 kilograms per year in 1985. During this period, the ratio of omega 6 to omega 3 in the diet increased from 4:1 to 25:1. Could this be a contributing factor to the increasing incidence of obesity? Determining your precise dietary fatty acid requirements is best accomplished with guidance of a blood test that measures fatty acid levels.

Avoid the partially hydrogenated vegetable oils, which function much like saturated fats in the body and have other adverse effects of their own. Foods that contain hydrogenated vegetable oils include margarine, shortenings, salad dressings, ice cream, fried foods, and most processed and baked goods, including breads, crackers, chips, cookies, cake, and candy. Read food labels to check for partially hydrogenated oils. Limit consumption of the foods high in saturated fats: beef, pork, lamb, egg yolks and dairy products (except for non-fat). When you do eat beef, purchase lower-fat cuts such as filet mignon and sirloin. Consider free-range beef, buffalo and ostrich, which have a more favorable fatty acid profile. A good choice for eggs is a brand by the name of Gold Circle Farms, which comes from hens fed algae. Each egg contains 150 milligrams of DHA.

Although consumption of beef and dairy should be limited because of their high saturated fat content, these foods ironically also contain a fatty acid that appears to aid weight loss. It is called conjugated linoleic acid (CLA). Importantly, CLA is available in purified, supplemental form. CLA activates a cell receptor that appears to be involved in increasing: insulin sensitivity, fatty acid transport into the mitochondria, energy expenditure, size and number of peroxisomes, and activity of fatty acid beta-oxidation enzymes. CLA influences enzymes that result in smaller fat cells. In one study, 60 overweight subjects were supplemented with either olive oil or varying doses of CLA. People getting at least 3.4 grams of CLA per day lost 2 to 3 pounds more weight than the others after three months. The group getting the highest dose of CLA (6.8 grams) had the added benefit of gaining lean body weight. Another study found 4 weeks of CLA reduced abdominal fat in middle-aged men with the metabolic syndrome (apple-shaped obesity). Yet another study found 60 days of CLA supplementation reduced cellulite and thigh circumference in women. Some studies, however, failed to find weight loss benefits from CLA. I don't recommend CLA for everyone as I do the omega 3 fats.